The effect of orange juice consumption on urinary pH was studied in seven adult male subjects, each of whom served as his own control. The diet of the subjects was standardized during the work-day. The effects of two regimens of orange juice were studied: 1500 ml divided into five 300-ml portions during the day, and 300 ml once in the morning. Urine was collected, its pH recorded, and titrated with HCl to determine the mEq of base excreted per unit time. The consumption of 300 ml of orange juice did not significantly alter urinary pH. The consumption of 1500 of orange juice changed the urinary pH by an average of one pH unit. A change of this magnitude could cause clinically significant variation in the overall excretion pattern of acidic or basic drugs.