Guinea pigs weighing approximately 300 gm were kept in a cold room, held at 6° C, for two weeks. Various organs were then studied histochemically. Liver glycogen is rapidly used up in cold-exposed guinea pigs . The fate of liver lipids is unknown. Lipids in the cortex of the adrenals appear to decrease, and chromaffin material in the medullary areas of the adrenals disappears. There is cavitation in the cortex and an erosion of medullary areas . There is increased metachromasia in the lower tubular areas of the kidneys, but the functional significance of this is not clear.