Gingival crevicular fluid, collected from 8 patients with chronic adult periodontitis before and 21 days after root planing and scaling, was analysed for prostaglandin E2, 6KPGF1 alpha, cAMP, IgG, IgM and alpha-2-macroglobulin, and their inter-relationship evaluated. There was a significant decrease in the levels of prostaglandin E2, IgG, IgM and alpha-2-macroglobulin after treatment, whereas the levels of 6KPGF1 alpha and cAMP remained essentially unchanged. The level of prostaglandin E2 decreased by 35%, IgG by 32%, IgM by 90%, and alpha-2-macroglobulin by 79%. There was a significant degree of correlation between prostaglandin E2 and 6KPGF1 alpha and cAMP before treatment but not after, but no correlation between prostaglandin E2 and IgG, IgM and alpha-2-macroglobulin either before or after. This correlation pattern indicates the involvement of E2, prostaglandin 6KPGF1 alpha and cAMP in inflammation in the periodontium. The changes in IgG, IgM and alpha-2-macroglobulin reflect yet another mechanism of host response which appears to be independent of prostaglandins.