The protein products of many dominant oncogenes are capable of inducing both cell proliferation and apoptosis. Recent experiments employing transgenic mice that express an ectopically regulatable myc gene or protein have begun to elucidate the role of the balance between proliferation and apoptosis in Myc-induced carcinogenesis. An outstanding feature of these experiments is the demonstration that the balance between oncogene-induced proliferation and apoptosis in a given tissue can be a critical determinant in the initiation and maintenance of the tumor.