Homogenates prepared from sections of human uterine cervix or endometrium were incubated with [1-14C]arachidonate and the products examined by radio-TLC. A major product chromatographing with 12-hydroxyeicosatetraenoic acid (12-HETE), and a number of more polar metabolites which were unaffected by 50 microM indomethacin but decreased to the same extent as 12-HETE by 50 microM nordihydroguaiaretic acid, were demonstrated by this technique. The addition of glutathione to the incubation mixture increased the production of 12-HETE, with a proportional decrease in the polar products. There was a large variation in 12-lipoxygenase activity measured in different cervix samples. The levels of the enzyme in the cervix were similar in two groups of uterine samples classified by the histological appearance of the endometrium as proliferative and secretory. However activity was significantly lower in samples taken from post-menopausal patients compared with pre-menopausal patients.