Overexpression of the apoptosis protection gene bcl-2 abolished the earliest response to serum withdrawal in NIH-3T3 murine fibroblasts, i.e., the abrupt cytoplasmic free calcium drop. This phenomenon, also observed in a myeloid cell line, led us to propose this ionic waving as an early apoptotic signal. Its abolition by bcl-2 overexpression suggests that this gene plays a role also on early events "priming" apoptosis.