In the present study, the expression of IL-1 receptor (IL-1 R) on the primary cultured hepatocytes was determined and the effect of IL-1 on the intracellular amount of cytochrome P-450 was investigated. The kinetics of IL-1R on the hepatocytes was studied by [125I]-IL-1 alpha and revealed that 5,000 molecules of IL-1 bound to a hepatocyte with a Kd of 4.0 x 10(-9) M. Incubation of the hepatocytes with IL-1 for 18 hrs decreased the contents of cytochrome P-450 in a dose-dependent manner. These findings suggest that IL-1 potentially depresses the drug metabolism involving IL-1R which is expressed on hepatocytes.