Describes Innovative Virtual Terminator™ Nucleotides for Single Molecule Sequencing

CAMBRIDGE, Mass.–Helicos BioSciences Corporation (NASDAQ: HLCS), a life science company focused on innovative genetic analysis technologies, today announced the publication of a seminal discovery in nucleotide chemistry for single molecule sequencing. The study, now appearing in the on-line edition of Nature Methods, demonstrates the synthesis and use of novel, fluorescently labeled, reversible terminator nucleotide analogs for use in single molecule DNA sequencing. These Virtual Terminator™ nucleotide analogs enable the accurate sequencing of single molecules of DNA by ensuring the step-wise incorporation of single nucleotides in homopolymer sequences. The article will appear in the August 2009 print issue of Nature Methods.

“Single molecule sequencing-by-synthesis presents major challenges and stringent requirements in terms of nucleotide chemistry,” said J. William Efcavitch, PhD, the company’s Chief Technology Officer. “The data in Nature Methods demonstrate that our nucleotides meet the requirements for robust, high-fidelity single molecule sequencing.”

Scientists at Helicos developed and tested a collection of modified nucleotides for incorporation efficiency, fidelity, termination ability and termination reversibility. The best analogs were subsequently used to accurately sequence a canine bacterial artificial chromosome (BAC) using the company’s single molecule sequencing technology. Due to the unbiased and accurate nature of the technology, >99% of the BAC was evenly covered with a very low per nucleotide error rate. Unlike amplification-based platforms, the Helicos system produces even error rates throughout virtually the entire length of every read, provides a very low substitution error rate, and does not suffer from significant %GC biases. This has major benefits for applications such as targeted resequencing and whole genome resequencing, for which accuracy and even coverage are of paramount importance.

“The creation of Virtual Terminator chemistry is another milestone in our development of innovative genetic analysis solutions for the research community, and is a testament to our leadership in the single molecule sequencing space,” said Steve Lombardi, President of Helicos.

The company has made sequencing data sets available on the HeliSphereTM Technology Center (http://open.helicosbio.com/), their open access Web site for sharing Helicos data sets and bioinformatics software tools.

About Helicos BioSciences:

Helicos BioSciences is a life science company focused on innovative genetic analysis technologies for the research, drug discovery, and diagnostic markets. Helicos’ proprietary True Single Molecule Sequencing, tSMS(TM), technology allows direct measurement of billions of strands of DNA enabling scientists to perform experiments and ask questions never before possible. Helicos is a recipient of the $1,000 genome grant and committed to providing scientists the tools to unlock the era of genomic medicine. The company’s corporate headquarters are located at One Kendall Square, Building 700, Cambridge, MA 02139, and its telephone number is (617) 264-1800. For more information, please visit www.helicosbio.com.

Certain statements made in this press release that are not based on historical information are forward-looking statements which are made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. This press release contains express or implied forward-looking statements relating to, among other things, the prospective commercial and scientific value of Helicos’ publication in Nature Methods discussed in this press release, and management’s plans, objectives and strategies. These statements are neither promises nor guarantees, but are subject to a variety of risks and uncertainties, many of which are beyond Helicos’ control, which could cause actual results to differ materially from those contemplated in these forward-looking statements. In particular, the risks and uncertainties include, among other things, our ability to successfully complete and/or scale the manufacturing and commercialization process for the Helicos Genetic Analysis System; our history of operating losses and ability to achieve profitability; our ability to sustain and scale our manufacturing capabilities; the research and development spending levels of academic, clinical and governmental research institutions and pharmaceutical, biotechnology and agriculture companies who may purchase our Helicos Genetic Analysis System; our reliance on third-party suppliers; competition; changing technology and customer requirements; our ability to operate in an emerging market; market acceptance of our technology; the length of our sales and implementation cycles; our dependence on large contracts for the sale and implementation of our Helicos Genetic Analysis System; failure of our technology and products; our ability to maintain customer relationships and contracts; ethical, legal and social concerns surrounding the use of genetic information; our ability to retain our personnel and hire additional skilled personnel; our ability to manage our growth while operating with limited resources; our ability to control our operating expenses; general economic and business conditions; our ability to obtain capital when desired on favorable terms; and the volatility of the market price of our common stock. Existing and prospective investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. Helicos undertakes no obligation to update or revise the information contained in this press release, whether as a result of new information, future events or circumstances or otherwise. For additional disclosure regarding these and other risks faced by Helicos, see the disclosure contained in Helicos’ public filings with the Securities and Exchange Commission.