Studies have shown that certain beverages decrease urinary lithogenicity by increasing urine citrate excretion. Diet Sunkist Orange soda had the highest concentration of citrate and total alkali content among 12 diet sodas previously assayed. We studied the effect of Diet Sunkist Orange soda consumption on urinary chemistry. Nine healthy men and women ages 26-54 years completed the study. During the control period, subjects drank 36 oz of water for 3 days in addition to their own, self-selected diet and recorded a food diary. During the study period, the subjects drank three 12-oz cans of Diet Sunkist Orange soda a day instead of water, and replicated their diets from the control period. In each period, the subjects performed 24-h urine collections on days 2 and 3. Urine chemical analysis was performed, including urinary citrate levels and pH. Diet Sunkist Orange soda increased urinary citrate excretion by 60 mg/day, which was not statistically significant (95% CI -75 to 195, P value 0.34). There was no significant change in pH from the control period to the study period (pH: 6.29-6.21; 95% CI: -0.09 to 0.25, P = 0.30). Urine volumes and creatinine excretions were not significantly different between the control and study periods. Despite the relatively high citrate and total alkali content of Diet Sunkist Orange soda, the volume consumed in this study (36 oz per day) did not provide sufficient potential base to significantly alter urine composition in healthy subjects with normocitraturia. The effect of Diet Sunkist Orange soda on urinary chemistry in patients with hypocitraturia and nephrolithiasis is not likely to have a clinically significant effect to prevent calcium or uric acid stones.