A monospecific antibody for human epidermal transglutaminase was prepared in rabbits. The antibody formed single immunoprecipitin lines with purified or crude human transglutaminases and quantitatively precipitated transglutaminase activity. There were no precipitin reactions between human factor XIII (zymogen or active enzyme) and antihuman epidermal transglutaminase or between human epidermal transglutaminase and antihuman factor XIII. Heating epidermal transglutaminase (56 degrees C, 15 min) in the presence of calcium increased the enzyme activity up to 10 times baseline levels. The heat-activated human epidermal transglutaminase was identical by immunodiffusion with the native enzyme, although slightly higher precipitation titers were detected following heating. There was no cross-reaction of antihuman epidermal transglutaminase with frog, rat, mouse, chicken, or human hair follicle transglutaminases.