Starvation for 48 h elicited a 74% increase in hepatic pyruvate dehydrogenase (PDH) kinase activity, measured directly by 32Pi-incorporation from [gamma-32P]ATP into a synthetic peptide corresponding to the major phosphorylation site on E1. The administration of chow ad libitum to previously-starved rats suppressed hepatic PDH kinase activity by only approx. 20% within 2 h of re-feeding, and the relatively high activity of PDH kinase was associated with continued suppression of PDC complex re-activation. Whereas there was no further decline in PDH kinase activity over the next 2 h, PDC re-activation to the fed value was observed during this time interval. PDH kinase activity decreased to fed values only after 8 h.