Abstract In the present study we investigate whether glucose concentration could have an effect on proinsulin biosynthesis and processing. We cultured control human islets under chronic high and low glucose concentrations. After the culture period, islets were pulse-labeled and chased for different periods of time. Proteins from islets were collected, insulin immunoprecipitated, and analyzed by alkaline–urea gel electrophoresis. We have found an accelerated rate of proinsulin conversion by those islets exposed to high glucose concentration (at 24.4mM of glucose), but not by those islets cultured at low glucose concentration (at 5.5mM of glucose). However, we do not observe any decrease or increase on newly proinsulin synthesis in any of these conditions.