Disclosed are a method of inducing apoptosis of a malignant cell, which employs a calcium-activated potassium channel (K.sub.Ca) activator and is useful for treating a malignant tumor in a human subject. Also disclosed are methods of selectively inhibiting the proliferation of malignant cells compared to non-malignant cells in a mixed population of malignant and non-malignant cells and of inhibiting the growth of a malignant tumor, such as a glial tumor, in a mammalian subject. A kit for inducing apoptosis of malignant cells is also disclosed.