This study was undertaken to determine the ability of inflamed and normal gingival tissues to synthesize prostaglandins (PGs) from the precursor arachidonic acid. Thirteen samples of inflamed human gingival tissue and six samples of normal human gingival tissue were studied. The inflammation was characterized histologically. After incubation of the tissue with [14C]arachidonate, PG metabolites were separated by thin-layer chromatography and identified by comparison with co-chromatographed standards. Inflamed gingival tissue synthesized significantly larger amounts, compared to normal tissue, of 6-keto-PGF1 alpha (P less than 0.05), thromboxane B2 (P less than 0.01), PGD2 (P less than 0.05), and PGA2 (P less than 0.001). Some unidentified metabolites, possibly lipoxygenase products were detected in significantly (P less than 0.001) larger amounts in inflamed than in normal tissue.