The effects of taurine on the motility and intracellular free Ca2+ concentration of fowl spermatozoa were investigated in vitro. The addition of taurine, within the range of 0-5 mmol l(-1), did not appreciably affect the motility of intact fowl spermatozoa. Motility remained almost negligible at 40 degrees C, while vigorous movement was observed at 25 degrees C. Even with the addition of Ca2+ before the addition of taurine, neither stimulation nor inhibition of motility was observed compared with the control (no addition of taurine). Similar results were obtained by the addition of taurine and calyculin A, a specific inhibitor of protein phosphatases. There were no changes in intracellular free Ca2+ concentrations, measured by a fluorescent Ca2+ indicator, fura-2, in taurine-treated spermatozoa. These results suggest that taurine is not involved in the regulation of fowl sperm motility and metabolism by intracellular Ca2+ mobilization in vitro.