Abstract: A novel method of inhibiting blood platelet aggregation is disclosed which comprises the use of a CAMP inhibitor together with an inhibitor of thromboxane synthesis. While inhibitors of thromboxane synthesis are only weak inhibitors of platelet aggregation, the addition of only a small amount of a CAMP inhibitor has been found to result in a synergistic increase in the degree of platelet aggregation resulting from such combined additions. Marked increases over the otherwise expected culumative effects of these inhibitors have been demonstrated using combination of various thromboxane synthetase inhibitors and various CAMP inhibitors.