The prevalence of antibody to Hepatitis D Virus (HDV) was determined in serum samples collected from 174 Manitoba residents between 1974 and 1986. Anti-delta was detected in five of 123 HBV-infected individuals for an overall prevalence of 4.1%. Three of 54 (5.5%) persons who were sampled in the period 1974-77 were anti-delta positive, as were two of 69 (2.9%) sampled between 1982 and 1986 (p greater than 0.05). Four of 31 (12.9%) acute hepatitis B patients, and one of 92 (1.1%) chronic HBsAg carriers were anti-delta positive. Three of four intravenous drug abusers were anti-delta positive, as compared to two of 69 who denied drug abuse (p less than 0.0005). In three of the four patients with acute delta hepatitis, anti-delta was detectable in convalescent serum only; all four patients made a complete clinical recovery. A possible false-positive reaction for anti-delta was observed in the serum of one of 51 HBsAg negative controls, a patient with acute hepatitis A who was negative for all hepatitis B markers. These results indicate that HDV has been present in Manitoba since at least 1974, though at a relatively low level, and that infection is strongly associated with intravenous drug abuse. Reliable detection of anti-delta in patients with acute delta hepatitis requires the testing of serial serum specimens.