In the present study, the activity of 3 functionally related enzymes, creatine kinase (CK), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) levels in the rest and flow gingival crevicular fluid (rGCF, fGCF) from patients with rapidly progressive periodontitis (RPP) and adult periodontitis (AP) were determined before and after periodontal treatment, including maintenance. When rGCF and fGCF mean enzyme levels were compared, rGCF was found to contain approximately twice as much enzyme levels than fGCF throughout the study. The findings of the present study revealed that both the rGCF and fGCF samples also contained higher CK, LDH, and AST levels than serum samples. Baseline clinical parameters and GCF enzyme levels presented a significant decline throughout the non-surgical and surgical treatment phases in both patient groups, with surgical treatment being more effective. Despite clinical stability, in the AP group levels of LDH and AST showed a tendency to increase in the third month, while enzyme levels still continued to decrease in the RPP group, who received additional antibiotics during the surgical phase. These findings suggest that GCF intracytoplasmic enzyme profile is related with periodontal status and successful periodontal treatment, in addition to clinical improvement, has a significant effect on this profile. Analysis of biochemical events, more specifically intracytoplasmic enzyme levels in GCF, are likely to offer a sensitive measure of periodontal pathology which may help in overcoming the existing limitations of clinical parameters. For this purpose, analysis of rGCF intracytoplasmic enzymes seems to be more beneficial. J Periodontol 1998;69:1155-1163.