Morphological and ultrastructural changes were studied in Ictalurus sp. barbel taste buds (TBs), exposed to sublethal concentrations (3 ppm) of sodium alkylbenzene sulphonate for periods varying from 3 to 15 days. No significant alterations were noted after 3 days while, after just 6 days damage began to appear. The blood vessels were dilated and larger, more numerous intercellular spaces were observed between the light and dark TB cells than were to be found in the controls, but the basal portion of the TB was unaltered. After 9-12 days the most prominent features were the rupture of the plasma membranes, loss of microvillar organization of the light and dark cells as well as an increase in cytoplasmatic vacuolization. The skin was damaged and the germinative layer of the epidermis appeared activated and its height had increased. About 30% of the TBs were affected, and after 15 days they were severely damaged, whilst the feeding behaviour changed from day 6 onwards.