The scrapie-infected hamster has been considered an excellent model for the study of slow virus diseases of man (Creutzfeldt-Jakob disease) and animals. At the moment no therapy is available for the cure of these fatal central nervous system diseases, although several drugs have been tested. We found that amphotericin B (AmB), a polyene antibiotic, increased the incubation time of scrapie disease in animals infected by either the intraperitoneal or intracerebral route. Hamsters inoculated with a 10% brain suspension of the 263K strain of scrapie showed clinical signs of disease in 54.6 +/- 4.7 days. Under AmB treatment (1 mg/kg for 6 days a week) the incubation time increased with the length of treatment, up to a maximum delay of 45 days. AmB may interact with the scrapie agent on cell plasma membranes and may thereby decrease the rate of scrapie replication. However, AmB did not have any effect when administered after the clinical onset of scrapie disease.