The effects of a number of prostaglandins on the metabolism of fructose by epididymal and ejaculated ram spermatozoa were investigated using conventional Warburg techniques. Spermatozoa from the two sources were collected concurrently during electrical stimulation; the epididymal spermatozoa were harvested via a cannula inserted chronically into one vas deferens and thus were free from exposure to the seminal prostaglandins. In general, the metabolism of fructose by the spermatozoa was little affected by a wide range of prostaglandins at a concentration of 20 micrograms/ml. Of the PGs present in semen, PGE2, PGE3 and PGF2alpha had no significant effects whereas PGE1 and PGF1alpha significantly increased lactate accumulation and the latter increased oxygen uptake, in both cases without significantly changing fructose utilization, fructose oxidized or CO2 production. Both 15-methyl-substituted PGE2 and PGF2alpha and their corresponding methyl esters failed to change fructose metabolism and it is unlikely therefore that the lack of response to PGE2 and PGF2alpha was due to their being metabolized by the spermatozoa during the incubation. Of a number of breakdown products tested, PGA1 and to a lesser extent PGA2 appeared to inhibit the Krebs tricarbocyclic acid cycle and 15-keto 13,14-dihydro-PGF2alpha appeared to stimulate it. In general, epididymal spermatozoa responded to the PGs in the same way as ejaculated spermatozoa. Thus we did not confirm a suggestion in the literature that spermatozoa have lowered sensitivity to PGs in vitro once they have been in contact with the PGs in seminal plasma.