It has been reportedly previously that complement enhances pemphigus vulgaris antibody-induced epidermal cell detachment. The present studies were designed to eliminate the possibility of the human plasminogen-plasmin system contributing to the cell detachment observed in previous complement-mediated studies. To assay for the presence of protease contamination in the reagents, a simple, sensitive, caseinolytic-fluorometric assay was used. Confluent murine or human epidermal cell cultures were incubated with pemphigus IgG with and without complement and plasminogen. Detached epidermal cells, as determined by light microscopy and cell-counter analysis, were enumerated at 48 hours. Incubating pemphigus IgG with complement resulted in marked cell detachment, compared with minimal cell detachment when pemphigus IgG was incubated with plasminogen. Culture media were collected after 48 hours and assayed for activation of plasminogen. It was determined that the added plasminogen had not been activated, particularly in experiments where significant detachment was observed. The plasminogen could still be activated by streptokinase and urokinase. These studies suggest that epidermal cell detachment in pemphigus appears to be mediated at least in part by complement activation.