There is evidence suggesting a role of eicosanoids in the growth of certain tumors. In this study, tissue samples were collected from basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) of the skin. Both BCCs and SCCs contained more prostaglandin E2 and F2 alpha (PGE2 and PGF2 alpha) than normal epidermis. In vitro incubation of tumor samples with arachidonic acid also resulted in PGE2 and PGF2 alpha formation. Basal cell carcinomas exhibiting a histologically aggressive growth pattern contained higher levels of prostaglandins than those with a nonaggressive growth pattern, both in vivo and after in vitro incubation. Lipoxygenase products (12- and 15-hydroxyeicosatetraenoic acid) were present in smaller amounts than cyclo-oxygenase products (PGE2 and PGF2 alpha) in vivo. Compared with normal epidermis, SCCs and, particularly, BCCs produced smaller amounts of 12-hydroxyeicosatetraenoic acid during in vitro incubation with arachidonic acid. The levels of lipoxygenase products were not related to the tumor growth pattern. These results indicate that excessive prostaglandin levels in BCCs may be associated with an aggressive growth pattern.