The effect of reduced temperature on the post-translational processing and stimulated release of von Willebrand factor (vWf) from human umbilical vein endothelial cells was studied. Following pulse-labeling, cells were incubated for 4 h at 18 degrees C or 20 degrees C. Post-translational processing was reversibly arrested at the dimer stage, dimers were composed of Endo H-sensitive precursor subunits, and no vWf was detected in the culture medium. This block was reversible, since warming cells to 37 degrees C relieved it and resulted in the appearance of fully processed vWf in the cells and the culture medium. The same results were obtained when cells were incubated with carbonyl cyanide m-chlorophenol hydrazone or dinitrophenol which inhibit mitochondrial oxidative phosphorylation, known to block exit of secretory proteins from the endoplasmic reticulum (ER). This indicated that ER exit is not required for the complete dimerization of vWf. Reduced temperature (18 degrees C and 20 degrees C) also reversibly and nearly completely inhibited the secretagogue-induced release of vWf from Weibel-Palade bodies without affecting the microtubular cytoskeleton. We add reduced temperature to the list of useful tools for the study of the vWf secretory pathway in endothelial cells.