Sensitive fluorogenic assays were used to compare the protease activities of fluid collected from eight such sites in each of 21 adult patients with gingivitis and 22 with periodontitis. The degradation of N-carbobenzoxy-gly-gly-arginine-AMC, L-arginine-AMC, glyproline-AMC, L-leucine-AMC, N-alpha-benzoyl-L-arginine-AMC, N-[p-toluenesulphonyl]-gly-pro-arginine-AMC, N-tert-butoxycarbonyl-leu-ser-thr-arginine-AMC, N-tert-butoxycarbonyl-ileu-glut-gly-arginine-AMC and N-tert-butoxycarbonyl-val-leu-lysine-AMC was significantly greater by fluid from the periodontitis group. The specific rates of degradation of L-arginine-AMC, gly-proline-AMC, N-alpha-benzoyl-L-arginine-AMC and N-[p-toluene-sulphonyl]gly-pro-arginine-AMC were significantly greater in that group, indicating that the composition of their gingival crevicular fluid was different from that of the gingivitis group. Discriminant analysis of the substrate hydrolysis data alone correctly identified 77.6% of sites with sensitivity and specificity values of 73.3 and 82.1%, respectively. The predictive value of these assays requires further investigation, but it is possible that they will prove useful for monitoring the success of periodontal treatment.