Abstract Sperm passing through the male tract interact with accessory sex gland fluids during ejaculation. Cellular metabolism is stimulated by this interaction for unknown reasons. These experiments involved calorimetric measurements [ P. B. Inskeep and R. H. Hammerstedt (1983) J. Biochem. Biophys. Methods 7, 199–210 ] on ejaculated sperm (EJS) and cauda epididymal sperm (CES) from bulls to establish the contribution of individual pathways to total cellular ATP synthesis. Parallel incubations outside the calorimeter yielded samples for oxygen consumption measurements and for motility analysis, the major ATP-consuming reaction of sperm. Energy charge values were identical for incubations of EJS and CES with glucose, thereby establishing that the ratios of rates of ATP synthesis and degradation were equivalent for these cells under this incubation condition. The total rate of ATP synthesis was greater for EJS than for CES (5 vs 13 μmol ATP h −1/10 8 cells) with <2 μmol ATP h −1 for each cell type coming from degradation of endogenous reserves. Thus, ejaculation is associated with a large increase in catabolic rate that is satisfied by degradation of extracellular glucose. No difference in percentage of motile sperm was noted, but mean velocity was lower for CES (58 μm s −1) than for EJS (85 μm s −1). A difference in forward motility pattern was observed (wig-wag to flipping). We conclude from these data that interaction with accessory sex gland fluids alters ATP requiring activities of sperm, with one obvious alteration being their motility pattern. The increase in ATP requirement is satisfied by increased degradation of extracellular substrates, but not intracellular reserves, to provide sufficient ATP to satisfy cellular needs.