Cimetidine was one of a variety of drugs frequently given to surgical patients perioperatively tested for their effect on gap closure of wounded monolayers of human fascia cells in vitro. Cimetidine-treated cultures closed faster and had greater cell proliferation than controls. Closure of cimetidine-treated cultures occurred at six hours compared to ten hours in controls. Cimetidine concentrations of 1000 micrograms/ml resulted in 13.5 +/- 0.67 (SEM) X 10(4) cells/cm2 at six hours compared to 7.9 +/- 0.48 X 10(4) cells/cm2 in controls (p less than 0.05); the area covered by cells was 6.5 +/- 0.02 mm2 in treated cultures compared to 3.0 +/- 0.01 mm2 in controls (p less than 0.05). It is concluded that cimetidine stimulates fibroblast proliferation in vitro.