Pancreatic lobules pulse-labeled with [3H]leucine have been incubated at temperatures between 0 and 37 degrees C in the presence or absence of ongoing oxidative phosphorylation. Subcellular fractionation methods and electron microscopic autoradiography have been used to monitor the progress of intracellular transport of newly synthesized secretory proteins. Over the period studied, exit from the rough endoplasmic reticulum (RER) occurs only at greater than 10 degrees C while traversal of the Golgi complex and entry into condensing vacuoles requires greater than 22 degrees C. Both steps of transport require ongoing ATP production. Incubation at 10 or 20 degrees C does not diminish ATP levels, relative to 37 degrees C controls. Remarkable and unprecedented alterations of the ultrastructure of transitional elements of the RER accompany the arrest of exit from the RER: at 10 degrees C transitional elements are much more numerous and longer than in controls; in the absence of ATP production they are essentially absent. These observations are interpreted in terms of a cyclic model of RER-to-Golgi vesicular traffic. Inhibition of ATP production also causes an increase in the rigid cisternae and coated elements in the distal Golgi area.