Parafilaria bovicola (Tubangui 1934), a filarial nematode, causes cutaneous bleedings of live cattle and bruise-like lesions in the subcutaneous and IM surfaces of affected carcasses. To determine the vector(s) of this nematode under Swedish conditions, a field survey was conducted during the pasture season, May-September 1980. A total of 9,931 insects were collected from cattle and subsequently examined for infective 3rd stage Parafilaria larvae. From the fly species collected. Musca autumnalis (De Geer), Hydrotaea irritans (Fall), and Haematobia stimulans (Meig) were those most frequently identified. The 3rd-stage larvae were only found in M autumnalis, face fly. Overall infection rate in these flies was 3.5%, with peak prevalence of 30% in June. Most of the nematode larvae were recovered from heads of female flies. In experiments in insect-free stables, 5 calves were experimentally inoculated with infective 3rd-stage P bovicola larvae. Two calves inoculated by the intraconjunctival route (larvae were instilled inside the eyelid) became infected, whereas 3 calves injected subcutaneously did not. Signs of infection were not seen in 4 control calves. The median development period of P bovicola from infective 3rd-stage larvae to the development of bleeding points was 43 weeks (301 days) in 26 cattle with spontaneous parafilariasis.