Homogenates of 5 neuroblastoma cell lines found to produce prostaglandin products from exogenous [14C]arachidonate, with specific enzyme activities ranging from 60 to 365 pmol per min per mg protein. Under identical conditions a glial cell line was much less active. PGF2 alpha and PGE2 were the major products from neuroblastoma cells, with PGF2 alpha predominating in all cases. The prostaglandin synthesizing activity of neuroblastoma extracts was at least an order of magnitude higher than activities reported for endogenous prostaglandin synthesis in brain tissues. The pattern of products was similar to that achieved after incubation of a rat brain microsomal extract with [14C]arachidonate, although the enzyme activity of neuroblastoma was about 200-fold higher. The presence of a relatively high prostaglandin cyclooxygenate activity in cultured neuroblastoma cells is of particular interest in that these cells may be useful model systems for studies of some aspects of neuronal prostaglandin synthesis.