Hepatitis B core antibody (anti-HBc) has recently been recognized as a paradoxical (surrogate) marker for non-A, non-B hepatitis agents in donated blood. We studied prospectively the hepatitis B virus antigen and antibody status and liver functions in 63 uremic patients admitted consecutively to our dialysis program. Nineteen percent of uremic patients, negative for hepatitis B surface antigen (HBsAg), hepatitis B virus surface antibody (anti-HBs), hepatitis B virus DNA, and antibody to delta agents, had anti-HBc in their sera at the time of admission to maintenance dialysis. This prevalence was significantly higher than that of the medical personnel working in the dialysis unit (P = 0.043) and healthy controls (P = 0.027). The prevalence of persistent presence of isolated anti-HBc increased to 31% in these uremic patients on long-term maintenance dialysis. Four patients had developed anti-HBc alone during their course of maintenance dialysis, and the appearance of anti-HBc was preceded by blood transfusion within 4 to 8 weeks. Transient or recurrent hepatic dysfunction occurred in three of these four patients. Patients with isolated anti-HBc were characterized by a higher incidence of repeated liver dysfunction (P less than 0.005), elevated alanine transaminase levels (P less than 0.005), and a higher transfusion requirement (P less than 0.01). Our data strongly suggest that these patients with isolated anti-HBc may have acquired either hepatitis B virus infection or non-A, non-B hepatitis through repeated blood transfusions despite careful screening of the donated blood to exclude transmission of hepatitis B virus.(ABSTRACT TRUNCATED AT 250 WORDS)