Iomai Corp., a Gaithersburg developer of vaccine-delivery technology, raised $54 million in a private stock offering, making it one of the region's best-funded young biotechnology firms.

The transaction is the Washington area's largest venture capital investment in the past year.

The private company will use the money to push its skin patches through the advanced human tests required for commercialization, Iomai chief executive Stanley Erck said yesterday. The company's technology -- using patches the size of a quarter to deliver a wide range of vaccines -- has shown encouraging results in patients and could offer a pain-free alternative to injections.

The size of the investment is unusual at a time when many biotechnology companies have been unable to raise money. In the late 1990s, biotechnology companies were able to raise billions through stock offerings and venture investors, but the cash flow stopped in 2000. There is little appetite now for new stock offerings, and fewer biotechnology venture capitalists are willing to bet on new products. The Iomai package is the largest biotech venture capital deal in the past six months, according to PricewaterhouseCoopers LLP's annual MoneyTree survey.

Iomai will issue Series C preferred stock to New Enterprise Associates, Essex Woodlands Health Ventures and MedImmune Ventures Inc., among others. The financing represents MedImmune Ventures' first investment in the biotechnology sector since the Gaithersburg-based company was created in July.

Iomai, founded in 1997, has raised about $80 million through corporate investors and venture capitalists, the company said. It is focusing its immediate efforts on an influenza vaccine patch, which is about to enter advanced human tests. Two other vaccines, for travelers' diarrhea and the bacterial infection tetanus, are in early-stage human tests.

Gregory M. Glenn, Iomai Corp.'s scientific director, holds a skin patch, which the biotechnology company uses to administer vaccines.