Methods for assessing functional consequences of olfactory mucosal damage were examined in rats exposed to 3-methylindole (3-MI). Treatment with 3-MI (400 mg/kg) induced severe degeneration of olfactory sensory epithelium followed by regeneration, fibrous adhesions and osseous remodeling of the nasal passages. At 100 mg/kg, there was mild Bowman's gland hypertrophy while the sensory epithelium remained intact. Rats treated with 3-MI demonstrated a dosage-related deficit in acquiring an olfactory learning task which was not due to altered cognitive abilities, as determined by subsequent testing in a step-through passive avoidance task. The results confirm the conclusion that alterations in functional indices resulted from 3-MI-induced anosmia and demonstrate the utility of simple learning tasks in assessing functional capacity following olfactory epithelial damage in rats. (Copyright (c) 1991 Academic Press, Inc.)