SummaryA 4 year survey was undertaken in 1982–6 to examine the seasonal nature of bluetongue virus activity in Malawi. Bluetongue infection at Bwemba in Lilongwe district and Likasi in Mchinji district, both in the Central Region of Malawi, was detected by examining sera taken from calves at each site, at monthly intervals. The proportion of seronegative calves undergoing serocon version each month was used as a measure of virus activity. At both sides bluetongue virus activity was found to be most marked during the rainy season, with no activity detected during the dry season from July to September. Thus the pattern of bluetongue infection in Malawi is highly seasonal. Examination of type-specific neutralizing antibody showed that the prevalent serotypes varied from year to year.