Decoquinate was tested for its ability to reduce the effect of experimentally induced toxoplasmosis in pregnant ewes. Sheep were given decoquinate in their feed daily at either 2 mg or 1 mg/kg bodyweight from 10 days before an oral challenge with Toxoplasma gondii oocysts at 90 days of gestation, until lambing. Feeding decoquinate at the higher rate caused a delay in the onset of the febrile response to infection, reduced the overall severity of the fever and delayed the production of antibodies to the parasite. This treatment also reduced the placental damage caused by the parasite, lengthened the mean gestation period and increased the number and weight of live lambs, in comparison with ewes not fed decoquinate but challenged with T gondii oocysts. The treatment with 1 mg of decoquinate had smaller effects.