To study the effects of changed synthesis on intracellular transport of secretory proteins, an acute phase response was induced in rats. The synthesis and secretion of haptoglobin, complement C3, transferrin and albumin were then investigated by pulse labeling with [3H]leucine. Maximal increase in the syntheses of the positive acute phase proteins was observed after 24 h, amounting to an increase of nine, three and twofold for haptoglobin, C3 and transferrin, respectively. The synthesis of albumin decreased to a minimum after 48 h, reaching approximately one fourth of normal synthesis. The time courses for transit through rough endoplasmic reticulum and for secretion were determined after 36 h, and were found to be roughly unchanged for all four proteins despite the different changes in synthesis. The fraction of haptoglobin associated with the microsomal membrane was reduced during the acute phase response, but there was no significant change in membrane association as a function of time after labeling with [3H]leucine. It is concluded that the altered protein synthesis during an acute phase response in vivo has little effect on the time course of secretion of the proteins studied. Furthermore, the basal mechanisms for intracellular transport appear relatively unchanged during this condition.