We conducted a seroepidemiological survey for antibodies to bovine leukemia virus (BLV), by using agar gel immunodiffusion technique, in dairy cows, water buffaloes, and yellow cattle throughout Taiwan. The positive reactors were 8.4% (376/4, 459) in 1985 and 5.8% (1, 277/22, 190) in 1986, in 15 prefectures and 7 cities. Relatively high infection rate appeared in the northern and southern areas of Taiwan. Positive reactors increased gradually with age. The incidence of positive antibodies was 2 to 3 times higher in pasture-style farms than in housed-style farms. Among the 6, 313 imported cattle, 302 (4.8%) showed positive reaction. Between 1985 and 1987, 5 cattle showed enzootic bovine leukosis among 351 sero-positive reactors in four highly positive prefectures. Survey of 134 water buffaloes and yellow cattle showed no positive reactors. This survey demonstrated that BLV-infection has increased over the years and spread throughout Taiwan.