This study was conducted to determine the influence of protein, vitamin B12 and choline on the systolic blood pressure of rats. Weanling rats were fed basal diets containing 10 or 25% protein and deficient in either vitamin B12 or choline. After 6 months on the basal diet, one-third of each dietary group was fed a diet containing 1% cholesterol, one-third was fed a diet containing 1% cholesterol plus 12% additional hydrogenated coconut oil and one-third continued on the assigned ration for the remaining 6 months of the experiment. Indirect systolic blood pressures were measured during months 9, 11 and 12 of the experiment. By averaging the blood pressure values of all three measurements, the male pressures were higher (P < 0.01) than the female, 130.8 and 124.1 mm Hg, respectively. The male blood pressures were greater for each determination than the female at 9, 11 and 12 months. The blood pressures and corresponding body weights for months 9 and 11 were correlated at the 1 and 5% level, respectively. All data were summarized as follows: males and females fed 25% protein, 131.3 mm Hg, and 10% protein, 123.6 mm Hg; males fed 25% protein, 136.7 mm Hg, and 10% protein, 125.0 mm Hg; and females fed 25% protein, 126.1 mm Hg, and 10% protein, 122.2 mm Hg. The 25% protein diet elevated the systolic pressure of the male rats. Cholesterol and hydrogenated coconut oil supplementation did not alter the indirect systolic blood pressure.