160 Romney ewes drenched with thiabendazole at 11 to 17 times the recommended dose resulted in 35 deaths. No deaths occurred in an equal number of undrenched ewes or in an equal number of ewes drenched with the recommended dose. Clinical signs, necropsy, histopathology and biochemical findings are reported. Deaths were associated with hypokalaemia, hypoproteinaemia and uremia, and were considered to have been the result of overdosage with thiabendazole.