Previous observations have shown unresponsiveness of pancreatic acini to cholecystokinin C-terminal octapeptide (CCK-8) and cholinergic agents in newborn rats. In this study, the possibility that a lack of protein kinase C may be one factor limiting the responsiveness of the acini was examined. In the term fetus and in newborns cytosolic protein kinase C activity was low. Shortly after birth, the activity increased rapidly and by 2 days of age reached adult levels which were 5-fold higher than that in the newborn. No differences in subcellular distribution of protein kinase C activity between the particulate and the cytosol fractions were found at any age studied. Developmental profiles of phorbol dibutyrate binding, an alternative method for measuring protein kinase C, were similar to those of protein kinase C activity measurements. Using stimulation of amylase secretion as an index of responsiveness, dispersed pancreatic acini of newborn rats were found to be unresponsive to TPA (a potent activator of protein kinase C) and CCK-8, but were responsive to dibutyryl cAMP and calcium ionophore A23187 (agents not dependent on protein kinase C activity). These results suggest that the low levels of pancreatic protein kinase C in newborn rats are at least in part responsible for the unresponsiveness of pancreatic acini to 12-O-tetradecanoylphorbol 13-acetate and CCK-8.