To study the immunological profile against the hepatitis B virus 742 sera (107 from the Renal Unit and 635 from other hospital services) were assayed for HBsAg, HBsAc, and HBcAc. The results obtained appear to indicate that the simultaneous determination of the three tests is unnecessary for diagnosis, although it is important for follow-up and prognosis. The isolated measurement of HBsAg is a good diagnostic test, but although it appears early it lasts little, a reason why it should perhaps be complemented with the other tests when considering the time factor. If only one technique is to be made available HBcAc determination seems necessary because it appears simultaneously with the HBsAg and it persists for a long time thereafter. A high degree of positivity of HBsAc and HBcAc was found in dialysis patients, a fact apparent also in the other population groups.