The effects of low dose indomethacin therapy in primary prevention of diet‐induced atherosclerosis of rhesus monkeys was studied. The parameters studied were serum cholesterol concentration, thromboxane A2 (T×B2), prostacyclin (6‐keto‐PGF1α) in serum/plasma, and the extent and intensity of coronary atherosclerosis. Although indomethacin did not affect scrum cholesterol, it reduced serum T × B2 significantly (P < 0.01). Plasma 6‐keto‐PGF1α was not restored to the pretreatment level. A significant protective role of the drug was noted as far as coronary atherosclerosis is concerned (P < 0.01).