To identify occupational categories and work areas of possible risk for acquisition of nosocomial hepatitis B by hospital personnel, serologic sampling for hepatitis B surface antigen (HBSAg) and antibody (anti-HBS) by radioimmunoassay was carried out in 513 employees of a large metropolitan hospital serving predominantly indigent patients. HBSAg was detected in 0.7%, HBSAg and anti-HBS in 0.4%, and anti-HBS in 13.3% of the study population. No significant difference in seropositivity was noted between sexes. Furthermore, neither exposure to patients with hapatitis nor previous blood transfusion correlated with serologic evidence of hepatitis B infection. However, frequency and intensity of exposure to blood products was associated with serologic evidence of infection: 18.9% of those with frequent blood contact were positive for HBSAg or anti-HBS, compared with 11.4% of those without blood product exposure (p less than .05). Direct patient contact, apart from blood exposure, did not appear operative as a major factor in hepatitis B transmission in this population. Accordingly, occupational categories and work areas with highest risk for acquisition of nosocomial hepatitis B were those with greatest blood exposure.