Skin explants maintained in culture may represent a reliable model for in vitro tests of the irritancy of chemicals. During the process of skin irritation intracellular enzymes migrate into the culture medium. The amount of released enzyme activity corresponds to the degree of skin damage. Skin of hairless mice (hr/hr) has been found to be especially useful for this model. Histomorphology demonstrated that the explants were almost identical to the in vivo situation. Skin explants of hairless mice of 50 mm(2) were used for the tests. The dermal side of the skin is in contact with the medium whereas the substance is applied to the epidermal side and incubated for 24 hr. As parameters for the membrane-damaging effect, the enzymes lactate dehydrogenase and glutamic-oxaloacetate transaminase were measured. The determination of the glucose utilization during the incubation period gave additional information about the viability of the cultured skin. Various chemicals were used. Histological examination complemented the biochemical results and differentiated epidermal lesions, but was limited by the absence of inflammatory reactions of the dermal part of the skin. Overall, in vitro skin culture tests seem to be useful as screening tests prior to in vivo studies and for the development of new formulations.