Voltage-dependent calcium currents (ICa) in cultured embryonic skeletal frog myocytes at the stages of development ranging from one to six days were studied using the whole-cell patch-clamp recording technique. Fast dihydropyridine (DHP)-nonsensitiveICa and slow DHP-sensitiveICa were recorded during the early stages of myogenesis. These currents do not differ in their kinetics from theICa found in the adult frog muscle. Two slow voltage-dependent DHP-sensitiveICa were found. In terms of its activation time, the first slow ICa is similar toICa described in phasic skeletal muscle fibers. The second slowICa observed in about 10% of cells examined is similar toICa described in tonic skeletal muscle fibers of adult frog. In some cases, two slow currents with different kinetics were recorded in the same myocyte.