Fasciolosis is recognised as a major problem in dairy cattle in Cajamarca, Peru. The infection has an annual cycle, with the major period of infection from January to March. A control programme, involving-two doses of the fasciolicide triclabendazole aimed at reducing the passage of Fasciola hepatica eggs on to the pasture, together with the use of the molluscicide, niclosamide, was evaluated against traditional treatment programmes. The double treatment regimen did not significantly reduce the overall parasite burden, as measured by faecal egg counts, but did control the parasites to a level similar to that achieved by traditional programmes averaging 3.7 treatments per year. The cows' eosinophil counts and serum liver enzyme activities were significantly lower than in animals treated by the traditional programmes. The use of niclosamide in addition to the triclabendazole treatments gave no clear advantage, although there was a significant reduction in the number of intermediate host snails after the application of the molluscicide.