Multiple myeloma and other hematologic tumors and/or malignancies can be treated by administration of a G1 and/or S phase drug, which is preferably .beta.-lapachone, or a derivative or analog thereof, combined with a G2/M phase drug such as a taxane derivative, which is advantageously paclitaxel. This combination of the G1 and/or S phase drug with the G2/M phase drug results in an unexpectedly greater than additive (i.e., synergistic) apoptosis in multiple myeloma cells. The invention includes methods of treating multiple myeloma by administering the combination of the G1 and/or S phase drug and the G2/M phase drug, pharmaceutical compositions comprising the combination of drugs used in these methods, as well as pharmaceutical kits.