Because serological markers (i.e., antigens and antibodies to those antigens, such as IgG and IgM) appear at various - predictable - times during the onset and course of an illness, they can serve as reliable indicators of the presence of the disease as well as its progression.

Examples of typical serological response to Epstein-Barr Virus (EBV), Hepatitis B Virus (HBV) and Human Immunodeficiency Virus (HIV) are depicted in the following charts.