A trypsinization technique was optimized for preparation of human epidermal single-cell suspensions from suction blisters. The conditions which provided the highest epidermal cell yield and viability was Sigma trypsin 0.25% (Type II, crude; cat. no. T8128). The incubation time should be 45 min at 37 degrees C with continuous shaking of the epidermal tissue. The use of suction blisters was evaluated for in vivo determination of epidermal thymocyte activating factor (ETAF/Il-1). Trypsinization of epidermis diminished ETAF/Il-1 activity. Dialysis of epidermal homogenates improves determination of ETAF/Il-1-like activity due to removal of low-weight inhibitors. Determination of ETAF/Il-1-like activity in homogenates of suction blisters constitutes a reliable model with acceptable reproducibility.