1. Deoxycorticosterone, which does not enhance tryptophan pyrrolase activity, also fails to alter the concentrations of the NAD(P) couples in livers of fed rats, whereas corticosterone increases both pyrrolase activity and dinucleotide concentrations. 2. Starvation of rats increases serum corticosterone concentration, lipolysis, tryptophan availability to the liver, tryptophan pyrrolase activity and liver [NADP(H)]. Glucose prevents all these changes. 3. The beta-adrenoceptor-blocking agent propranolol prevents the starvation-induced lipolysis and the consequent increase in tryptophan availability to the liver, but does not influence the increase in serum corticosterone concentration, liver pyrrolase activity and [NADP(H)]. 4. Actinomycin D, which prevents the starvation-induced increases in liver pyrrolase activity and [NADP(H)], does not affect those in serum corticosterone concentration and tryptophan availability to the liver. 5. Allopurinol, which blocks the starvation-induced enhancement of pyrrolase activity, also abolishes the increases in liver [NADP(H)], but not those in serum corticosterone concentration or tryptophan availability to the liver. 6. It is suggested that liver tryptophan pyrrolase activity plays an important role in NAD+ synthesis from tryptophan in the rat.