Peritoneal endometriotic implants and adjacent normal peritoneum from five patients were analyzed for prostaglandin (PG) release. Each tissue biopsy was incubated using medium 199 in triplicate at 37 degrees C for six hours, and PGF2 alpha and PGE2 concentrations were measured in the incubation medium every two hours. This study demonstrates that peritoneum involved with endometriosis releases significantly more PGF2 alpha and PGE2 (P less than .05) than adjacent normal peritoneum, and suggests that peritoneal endometriotic implants may be a source of the elevated peritoneal fluid PG levels previously reported in patients with endometriosis.