On the basis of inhibitory analysis by using a fluorescence probe chlortetracycline, calcium transduction pathway in spermatozoa of Bos taurus has been examined. Additional release of Ca2+ from intracellular stores of sperm was found after combiened action of prolactin and GTP, which took place under influence of protein kinase C inhibitor (compound Ro 31-8220); the combined effect of theophylline and GDP also stimulated additional release of Ca2+ from intracellular stores, which was missing when adding inhibitor of protein kinase A, compound H-89. Using chlortetracycline test (analysis localization of chlortetracycline fluorescence in spermatozoa), we have shown the combined action of prolactin and GTP increases the number of sperm with acrosome reaction, which is reduced after influence of Ro 31-8220; the combined effect of theophylline and GDP increases the percentage of capacitated spermatozoa, which was decreased in the presence of H-89. According with the data obtained, we propose the hypothesis that the transduction of Ca2+ between intracellular stores in bull spermatozoa stimulated by the combined action of prolactin and GTP, or theophylline and GDP, determines the functional status of the spermatozoa. Namely: the transduction of Ca2+ between intracellular stores in bull spermatozoa stimulated by the combined action of prolactin and GTP is involved in the regulation of acrosomal processes, while sperm capacitation is mediated by the transduction of calcium between intracellular stores activated by the combined influence of theophylline and GDP.