By means of modern tissue-culture techniques, photomicrography, and time-lapse microcinematography, evidence was obtained that cellular effects of narcotic addiction are not restricted to the central nervous system. Other cells, eg, human epithelial-like cells, can develop tolerance for and physical dependence on morphine sulfate (MS). Marked degenerative cellular changes occurred after prolonged exposure to MS; but cytoplasmic activity appeared unimpaired as long as the nutrient medium contained MS in effective concentrations.