The history of 20th-century architecture abounds with buildings that critics love and users hate, but there aren't many that have suffered such extreme public mood swings as the Richards Medical Research Laboratory at the University of Pennsylvania.

Designed by the acclaimed Philadelphia architect Louis Kahn, the clutch of brick towers was celebrated in a solo show at New York's MoMA in 1961, a year before it opened. The museum deemed Richards "the most consequential building constructed in the United States" since World War II.

The dirty secret is that Penn's scientists hated Richards from the day they moved in. They complained there was no privacy in the large, open-plan labs, and no respite from the natural light that flooded in from Kahn's generous windows. When papering the glass with computer printouts didn't solve the problem, scientists fled in droves, and Richards became a place where, as Penn's university architect David Hollenberg so delicately put it, "people who had less prominence found themselves."

I suspect the pecking order is about to be reversed now that Hollenberg's office has finished renovating two of Richards' four towers. Having long ago acknowledged that Kahn's masterpiece wasn't right for sensitive experiments involving bubbling beakers of chemicals, Penn decided to convert the complex into offices and computer labs for researchers.

The renovation - executed by a large cast of architecture and engineering firms - has stripped the labs of their manic clutter, banishing the mess of ventilation hoods, ad-hoc walls, and tangle of overhead pipes, which were notorious for leaking.

Removing those accretions was just the beginning. Hollenberg's team has cleaned all the concrete, giving it the glow of travertine, and replaced every window. After much debate, Hollenberg says they decided against installing energy-efficient insulated glass, which would have changed the building's look, and opted for thicker glass plates. They've carefully restored the elegantly thin window frames that give the jutting office windows their distinctive crisp corners.

Though a large part of each floor remains an open work area, Penn did insert a few private offices. But glass partitions help maintain the natural light in the common area. The windowless "servant" towers now house coat closets, kitchens, and seminar rooms.