Successful protection was obtained with interferon treatment in experimental viral infections in the bovine species in a number of cases. The efficacy of the treatment against vaccinia virus infection and against rotavirus infection have been demonstrated. On the contrary, bovine herpes virus 1 (BHV 1-causing rhinotracheitis and part of the shipping fever complex) infections were not inhibited by interferon (IFN). The authors have undertaken a study in cattle in Zimbabwe to assess the role of interferon in the resistance of the animals to Cowdria ruminantium. A good correlation between production of interferon by the animal following the infection, and the resistance of the animals against the rickettsia was demonstrated. This pointed out the possible "adjuvant" role of interferons and other cytokines.