Highly sensitive and specific radioimmunoassays for cholylglycine, chenodeoxycholylglycine, deoxycholylglycine, and sulfolithocholylglycine have been used to study the kinetics of the enterohepatic circulation of these conjugated bile acids in 8 healthy subjects. Venous blood samples were collected over a 32-hr period, during which time the subjects ate three meals. Serum levels of cholylglycine and chenodeoxycholylglycine rose after each meal, and reached their maximum level within 30 to 60 min. A second chenodeoxycholylglycine peak occurred 2 to 3 hr after the first two meals in all subjects; a second peak was also found for cholylglycine in 3 of the 8 subjects. Serum deoxycholylglycine levels also rose postprandially; the peak level generally occurred 30 min later than that of cholylglycine. Serum sulfolithocholylglycine levels did not alter significantly after meals. The data indicate that the dynamics of the enterohepatic circulation of individual serum bile acids differ both quantitatively and qualitatively.