In order to study the relation between prostaglandin F2 alpha levels and fever during Toxoplasma gondii infection, six non-pregnant ewe lambs were exposed orally to T. gondii oocysts and an additional four animals were used as non-inoculated controls. Rectal temperature was measured daily during four weeks and plasma samples were analysed for the content of 15-ketodihydroprostaglandin F2 alpha. As compared to controls, the inoculated animals had significantly elevated rectal temperatures on days 4-16 after infection, but no concomitant changes in prostaglandin F2 alpha metabolite levels were recorded.