The paper deals with the cadmium effects on the intestinal mucosa of adult Carassius auratus after 7, 14 and 40 days of exposure. After 7 days the mucosa becomes oedematous; the mucous cells show intensive secretion. The cells showing immunoreactivity for the Met- and Leu-enkephalin miss this feature. After 14 days these modifications diminish and after 40 days disappear completely and the mucosa gains its normal characteristics.