Viral hepatitis has become a difficult field in which clinical and laboratory skills are needed to establish the correct diagnosis and plan for the appropriate therapy. For example, it is no longer enough to diagnose chronic hepatitis B or C. Now, the viral titer or vital genotype must be known. The laboratory test then must be understood in the context of the clinical presentation. This article helps the clinician to acquire such working knowledge. It summarizes available data for hepatitis A, B, C, D, and E. It also includes the recently discovered vital agents, hepatitis G and the hepatitis GB agents.