The effects of protease inhibitors on cell dissociation were studied in vitro in order to examine the involvement of proteases in stratum corneum desquamation. Stratum corneum sheet (peeled from human backs after sunburn) was incubated in a detergent mixture containing 8 mM N,N-dimethyldodecylamine oxide, 2 mM sodium lauryl sulphate and 60 micrograms/ml kanamycin with or without protease inhibitors, and the number of released cells was counted after incubation for 48 h. Cell dissociation was inhibited strongly by antipain or aprotinin, but not at all by N-[N-(L-3-transcarboxyoxiran-2-carbonyl)-L-leucyl]-agmatin, N-ethylmaleimide or pepstatin, which suggests that only serine proteases are associated with desquamation. Furthermore, leupeptin and chymostatin each reduced cell dissociation about half as effectively as aprotinin or antipain, while a mixture of leupeptin and chymostatin prevented stratum corneum dissociation as potently as antipain or aprotinin. In addition, the activity of chymotrypsin-like protease in scaly skin was higher than that in normal skin, as we have previously found for trypsin-like protease. These results suggest that both trypsin-like and chymotrypsin-like serine proteases are involved in stratum corneum desquamation.