The technique of postosmication has been applied to resting and histamine-stimulated cells in the submucosal glands of the fowl proventriculus. In resting cells, the smooth endoplasmic reticulum, the mitochondria, and occasional vacuole-containing bodies become impregnated, but the Golgi apparatus, or ‘Dalton complex’ remains unaffected. In stimulated cells, the degree of impregnation of the smooth endoplasmic reticulum and vacuole-containing bodies is increased, and more mitochondria become heavily impregnated, but the Golgi apparatus remains unaffected. The significance of these observations is discussed.