Serum levels of CA 125 and other selected tumour markers were measured in 31 patients with proven pelvic inflammatory disease (PID). Ten (32%) of the patients had elevated CA 125, one (4%) had elevated CEA, and none had elevated CA 15-3, AFP or beta 2-microglobulin. Compared to patients with normal CA 125, patients with elevated CA 125 were older, more often users of intrauterine contraceptive devices, had longer duration of symptoms, higher erythrocyte sedimentation rates, and more often had an adnexal mass on pelvic examination. There was a correlation between CA 125 levels and the severity of adnexal inflammation as defined by laparoscopy. Isolation of specific micro-organisms from the upper genital tract was not associated with elevated CA 125. In most women serum levels of CA 125 decreased during treatment. PID should be considered as a major cause of positive CA 125 findings among young women.