The efficacy of 5-chloro-2-methylthio-6-(1-napthyloxy)-1H-benzimidazole was evaluated with three commercial fasciolicides in terms of the percentage of egg reduction in cattle. Fifty Swiss cows were selected for inclusion in the trial based on finding eggs of Fasciola hepatica in their feces. On day 0, they were blocked in five groups (G) of ten animals each according to fecal egg counts. G1 received compound alpha at 12 mg/kg p.o.; G2 triclabendazole at 12 mg/kg p.o.; G3.closantel at 3.5 mg/kg s.c.; G4 clorsulon at 2.0 mg/kg s.c. G5 animals served as untreated controls. Fecal analysis was performed on days 0, 7, 14, 21, 28, 60 and 90. Efficacy was measured on days 14 and 21. In addition, the extension and intensity effects were determined on day 60. The percentage efficacy for groups 1-4 was 98.1, 98.7, 98.2 and 97.9 on day 14 and 98.5, 97.9, 97.7 and 97.9 on day 21, respectively. No statistical differences were observed between treated groups.

The efficacy of 5-chloro-2-methylthio-6-(1-naphthyloxy)- 1H-benzimidazole, called "alpha", was tested against Fasciola hepatica. Fluke-free calves ( n=32) were divided into 8 groups and infected with 150 metacercariae per animal. All animals subsequently received a second infection with another 150 metacercariae, given at different time intervals aimed to produce flukes of differing ages within the experimental animals. When the flukes reached the required age in the animals, four groups were treated with a single oral dose of 12 mg/kg of compound alpha and the remaining ones served as non-treated controls. Two weeks after treatment the animals of all groups were sacrificed and the livers were removed to determine the numbers of parasites present in the treated and untreated controls. In the treated groups the fluke reduction for the 3 day/2 week group was 100%, for the 3 week/4 week group it was 96.4%, for the 6 week/8 week group it was 99.2% and for the 10 week/12 week group it was 100%.