"It's way behind schedule," says McMahon. "No one can tell me when it's going to be finished."

And for researchers whose delicate experiments depend on such a facility and the rodents it supports, such delays are no joke. McMahon and Robertson must commute to the larger Medical School mouse facilities in Boston, which house 30-40,000 mice.

"We're sort of twiddling our thumbs," says McMahon. "To do experiments when you have to commute five miles each way is not the ideal situation."

The two professors were tenured as a team in the spring of 1992, and a new mouse facility on the FAS side of the Charles River was definitely part of the package, McMahon says. "Neither of us of course would come unless there was a first-class mouse facility," he says.

Mice are the best experimental option because their physiology and in utero developmental processes have many similarities to that of humans, McMahon says. Mice also breed quickly and in fairly large litters, shortening experimental periods.

But at present, the research is on hiatus, waiting for the complex mass of wires, scaffolding and hidden machinery sitting on top of the Bio Labs to become a complete facility.

Inspectors from the City of Cambridge arrive unannounced about four times a year, he says, as do National Institutes of Health inspectors.

And the exactness of the construction is also important because small glitches can endanger any experiment. Deegan recalls one professor, who, for reasons still unexplained, lost his frogs and with them an experiment in progress. Perfect maintenance with delicate balances is necessary for Harvard's legions of experimental guinea pigs, rats, ants and toads as well, he says.

But amid the high-tech, spotless feeling of an advanced scientific laboratory there will be a small, poignant reminder of the everyday: Mousetraps will be stationed around the facility to prevent "Mrs. Frisby and the Rats of NIMH"-like breakouts so that none of the valuable subjects can escape.