A total of 32 042 cattle, slaughtered at the Pretoria, Johannesburg and Durban abattoirs, was examined for parafilariosis and as many animals as possible were traced to the farms from which they originated. The disease is most prevalent in the Bushveld areas of the northern Transvaal. The most important factors limiting its distribution are the annual rainfall and the duration of the frost period. Mention is made of some aspects of the economic loss involved. The effect of routine anthelmintic treatment and dipping on the prevalence of the parasite is briefly discussed.