These activities were measured simultaneously, using synthetic fluorescent protease substrates, in gingival crevicular fluid collected at 6 pre-determined sites from 10 individuals with mild to moderate gingivitis. The three enzyme activities were detected in 85, 18 and 93% of the sites, respectively. The volume of fluid collected from discrete sites was significantly correlated with the total amount of substrate hydrolysed, but not with the specific rate of substrate hydrolysis. Log10 (total trypsin-like activity) was significantly correlated with the Gingival Index, Plaque Index and probing depth (r = 0.319, 0.423 and 0.336), while total glycylprolyl dipeptidase activity was significantly correlated with probing depth (r = 0.381). These findings add to knowledge of the biochemistry of gingival crevicular fluid, but the usefulness of such assays for diagnostic or monitoring purposes in periodontal diseases needs to be determined.