The baculovirus of Thymelicus lineola (Ochs.) has proved most effective as a microbial control agent of its host in numerous field trials, however, prior to its general use in an integrated control programme its possible deleterious effects on non-target organisms must be considered. Therefore the pathogenicity of this baculovirus to sheep and its cytopathogenicity to tissue cultures of lamb and calf testes were studied. Preliminary tests on 16 insect species were also carried out. No macro- or microscopic differences were detected between treated and control groups, suggesting that this baculovirus is quite specific and that its use as a microbial insecticide is feasible against T. lineola.