The response of serum citrate to the oral citrate load was studied in seven healthy subjects. Serum citrate was significantly elevated from 15 to 60 min post-load with some individual variations. In 27 stone-formers serum citrate and the response to the oral citrate administration was studied and compared with the results obtained on healthy subjects. The serum citrate concentration of stone-formers was 1.99 +/- 0.49 mg/dl as compared to 1.61 +/- 0.35 mg/dl in healthy subjects. After citrate administration serum citrate increased significantly in both groups, but no significant difference was shown in response to the oral citrate load between these two groups (3.44 +/- 0.94 mg/dl in stone-formers, 3.16 +/- 0.38 mg/dl in healthy subjects). In Sprague-Dawley rats each weighing about 200 g urinary citrate and calcium excretion were studied after administration of sodium citrate or calcium chloride or both. The concomitant equimolar administration of sodium citrate and calcium chloride did not have significant influence on urinary citrate or calcium excretion as compared when citrate or calcium was given alone. However, the calcium excretion was significantly decreased with the administration of citrate and calcium ata molar ratio of 1:2.