MADISON, WIS. - If a mathematical equation could demonstrate the commercial vitality of stem cells, it would probably look something like this: Hype/Reality=Anxiety.

For all of the ooohs and ahhhs on display at last week's World Stem Cell Summit, there was also a prevailing sense among some investors and industry officials that all of this great technology must soon put up -- or shut up.

"We have to hit milestones with the public in order to sustain our momentum," said Linda Powers, co-founder and managing director of Toucan Capital in Bethesda, Md., a venture capital firm that invests in stem-cell start-ups. "This is a relatively young discipline, but there is a [large] amount of hype and expectations. When will the public's expectations expire?"

Despite tantalizing chatter about treatments and even cures of diseases such as Parkinson's, cancer and heart failure, the prospect of a stem-cell company actually selling real products and making real profits has never seemed so distant. Amid high development costs, lengthy approval times and skeptical investors, a sobering reality emerges.

Commercialization is "excruciatingly slow," said Michael Haider, CEO of BioE Inc., a St. Paul company that extracts stem cells from blood in human umbilical cords. "I'm not aware of a successful stem-cell company. If you thought gene therapy was difficult, then [stem cells] are astronomically difficult."