A competitive and a sandwich enzyme linked immunosorbent assay (ELISA) were developed for human leukocyte collagenase and gelatinase. The competitive assay could detect 0.5 ng collagenase and 0.05 ng gelatinase. The detection limit of the sandwich ELISA was 0.05 ng for collagenase and 0.02 ng for gelatinase. No cross reactivity between human leukocyte collagenase and gelatinase was detected. The sandwich ELISA was used to determine plasma levels of these enzymes. The 90% range for collagenase was between 0 and 50 micrograms/l; the 90% range for gelatinase was between 27 and 94 micrograms/l.