Experimental gingivitis provides a useful model for studying the initiation of periodontal disease in man. This study evaluated over a 4-week period the Plaque Index (PLI), Gingival Bleeding Time Index (GBTI), and gingival crevicular fluid (GCF) for resting and flow volume as well as the concentration and total activity of three enzymes in the GCF (lactate dehydrogenase--LDH, beta-glucuronidase--BG and arylsulfatase--AS) from the maxillary right quadrant of eight subjects with healthy gingiva. After rising sharply during the 1st week, the PLI continued to increase during the 2nd week but remained constant during the 3rd and 4th weeks. The GBTI, and the resting and flow GCF volumes, increased steadily throughout the study. LDH concentration in GCF varied minimally during the experiment, while total LDH activity rose slightly over the 4-week period. BG concentration and total activity in GCF rose steadily from baseline to the 3rd week and then either fell or leveled off during the 4th week. AS concentration in GCF rose from baseline to the 2nd or 3rd week and then fell. AS total activity in GCF rose from baseline to the 2nd week and then remained constant. These data suggest that while clinical signs of inflammation increased over the 4 weeks of the experiment, a homeostatic mechanism in the crevicular environment may control ground substance-degrading enzyme activity during experimental gingivitis in man.