Following a period of waning confidence in University startup companies, technologies spawned on Yale’s campus are making a comeback.

Last Friday, University officials announced that Yale will help launch a company to develop treatments for varicose veins, based on technology invented by School of Medicine professor Michael Tal. That same day, Yale startup company Achillion Pharmaceuticals, which specializes in infectious diseases, filed to sell up to $75 million in stock at an initial public offering. And today, a neuroscience pharmaceutical company, co-founded by a Yale professor and his student, will be showcased as a “featured success story” at a forum where experts will discuss ways to bring innovative concepts into the commercial market.

The past week’s successes for University startup companies were not out of the norm, officials from the Office of Cooperative Research said, but they reflect a growing demand for Yale ideas in fields in which investor interest has languished in recent years. Administrators said they hope royalty revenue from the University’s inventions — described as an important but unpredictable part of the science budget — will continue to rise in coming years. But some people familiar with the University’s approach to commercialization said Yale should be providing more support to professors who want to branch out into the for-profit sector.

Bill Wiesler, Yale’s associate director of cooperative research, said Yale’s startup businesses have made a comeback since 2003 and 2004, when an economic downturn took a toll on small development companies.

“Investors were not inclined to start new companies when the companies they had funded already were struggling to make ends meet,” Wiesler said. “Quite an enormous number of investor capitalists have raised new funds and have a fresh perspective on their willingness to get new companies started.”

Yale-affiliated entrepreneurs launch between three and five new startups per year in New Haven, mostly in the biomedical fields, Wiesler said. The University’s business partners — often private startups founded by professors and others affiliated with the University — currently pay royalties on several hundred licenses. But 80 to 90 percent of the revenue generated in a given year often comes from a single product, Wiesler said.

Zerit, a highly successful AIDS drug, is responsible for much of the last decade’s profits, Deputy Provost Charles Long said.

“You get a lot of singles and every now and then you get a home run,” Long said. “A lot of them don’t pan out at all.”

The revenues are usually split between the department where the technology was invented, a science development fund that supports research activities for new faculty, and the OCR itself, Long said. Though the money can serve as a valuable resource for researchers, he said, it represents a small fraction of the total University operating budget.

Yale officials and industry experts said commercial interest in university technology is growing, but they agreed that venture capitalists are now less inclined to risk their money in young technologies that require years of expensive testing before they are marketable. They are more interested in finding alternative uses for existing drugs, biology professor Vincent Pieribone said. Pieribone cofounded Marinus Pharmaceuticals, the company that will be featured as a success story at an industry event this week.

“The venture capital business seems to have been completely turned off to the idea of a company that set out to develop drugs,” Pieribone said. “Instead, they find a good drug and make 10 copies of it.”

But the investment climate is not the only obstacle to bringing Yale technologies to the market, Pieribone said. Yale does not offer as much support to startup companies as do some other schools, he said, citing Columbia University’s provision of “incubator” laboratories to help startups get off the ground. The University should also encourage professors to enter the commercial field by providing extra tenure consideration for commercially innovative scientists, Pieribone said, but he said many Yale faculty members view startup founders as sellouts.

“There is a distrust for professors involved in commercial endeavors,” he said. “That was the biggest disappointment.”

Long said the University does not offer special rewards for commercial activity because it is not as important to Yale’s mission as basic research.

Ashley Stevens, director of technology transfer at Boston University and a former official at the Association of University Technology Managers, said Yale surpasses many of its peers — including Harvard University and the Massachusetts Institute of Technology — in its support for startup companies.

“My impression is that Yale is a lot more hands-on, if the professor wants help, than many other institutions are,” Stevens said.

An AUTM survey reported that U.S. universities launched 425 startup companies last year — a record high — and collected more than $1 billion in license revenues.