We studied the prevalence and significance of antibodies to hepatitis C virus (HCV) in patients and staff from 3 dialysis units, using a 2nd generation assay (2nd g.a.; Ortho HCV). Of 277 patients, 151 (55%) were positive by 2nd and 85 (31%) by 1st g.a. Significant associations with the anti-HCV carrier status were: blood transfusions, retrospective finding of elevated ALT and duration of dialysis treatment, independently of transfusions. Of the 74 staff members, 5 were positive by 2nd and 3 by 1st g.a. Our data suggest that the 2nd g.a. is more sensitive in detecting HCV exposure in dialysis units and that duration of dialysis is a significant factor in acquiring HCV infection.