The effects of subchronic administration of captafol were studied in B6C3F1mice given dose levels of 0, 0.3, 0.625, and 1.25% in the diet for 12 wk. There was a dose‐related decrease in body weight gain during the 12‐wk experiment and a loss of body weight in the 1.25% group of both sexes. Whiles the mice given captafol consumed less diet than the control mice, this was not directly dose‐related. The relative weights of liver demonstrated a tendency for dose‐dependent increase. Light‐microscopic examination revealed cytoplasmic vacuolar degeneration, depending in severity on the dosage, in the livers of both sexes given captafol. In conclusion, the findings obtained from the present subchronic toxicity study indicated the liver to be a primary target organ.