In separate experiments, we fed 30 male and 25 female baboons a diet enriched in cholesterol and saturated fat for periods of 3.3 and 2.6 years. Using operant conditioning with water rewards, we trained the animals to puff on smoking machines in a human-like manner. Half of the animals smoked more than 40 cigarettes per day, while the remaining animals (controls) puffed air. Initially, the diet produced twofold (males) and threefold (females) elevations from baseline levels in serum cholesterol concentrations, but over the course of the experiments, the serum cholesterol decreased to 1.5 (males) and 2.0 (females) times baseline levels in both cigarette smokers and controls. Blood carbon monoxide concentration, plasma thiocyanate concentration, and urine cotinine concentration were significantly greater in smokers than in controls. Responses to smoking in males included lymphocytosis, elevated fasting blood glucose concentration, and decreased seminal vesicle weight. In females, hemoglobin and mean corpuscular hemoglobin concentrations were elevated. The extent of atherosclerosis was examined after 2.8 (males) and 1.6 (females) years of smoking. Among males. the extent of lesions in carotid arteries was significantly greater in smokers than in controls, but there were no significant differences in atherosclerosis in the aorta or the brachial, iliac-femoral, or coronary arteries. Among females, there were no significant differences in atherosclerosis between smokers and controls in any artery. These experiments show little effect of 2 to 3 years of cigarette smoke inhalation and concurrent modest elevation of blood carboxyhemoglobin on experimental atherosclerosis in the presence of moderate hyperlipidemia.