Several reactions of the Ist and IInd phase of biotransformation have been reported to be under a negative cyclic-AMP dependent control. Conjugation of bilirubin and glucuronidation of morphine were investigated in isolated mouse hepatocytes and in mouse hepatocyte microsomes, respectively. N6,O2-dibutyryl cyclic-AMP did not inhibit conjugation of bilirubin in isolated hepatocytes. ATP and the dissociated catalytic subunit of the cyclic-AMP dependent protein kinase did not influence the glucuronidation of morphine, while inhibited the formation of p-nitrophenol glucuronide in microsomes prepared from isolated mouse hepatocytes.