Studies conducted over the past 45 years have shown that immunoglobulin (IG) prevents 80%-90% of cases of hepatitis A when administered before exposure or shortly thereafter. Protection is short lived and requires early diagnosis and timely administration of IG to contacts. Inactivated and attenuated hepatitis A virus (HAV) vaccines have recently been developed and should be available for clinical use within the next few years. Evaluation of antibodies to HAV in IG and in IG recipients provides one method of determining the immunogenicity of HAV vaccines. The role of IG in the prevention of hepatitis A is reviewed with emphasis on the relationship of antibody response following IG administration to the efficacy of HAV vaccines.