A search for rickettsial antibodies in human sera from Central America was performed by complement-fixation and microagglutination tests. Over 2,000 human sera from Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, and Panamá were surveyed for antibodies against Rickettsia prowazeki, Rickettsia typhi, Rickettsia rickettsi, Rickettsia canada, and Coxiella burneti. The results of the survey indicated that: Q fever was endemic in Central America; in areas of Costa Rica, Honduras, and Panamá a small percentage of the inhabitants had spotted fever group antibodies; Rickettsia akari infections may have occurred in Costa Rica; epidemic typhus has been a major cause of rickettsial disease in the highlands of Guatemala. A low incidence of murine typhus was also found in Guatemala. Antigenic relationships between R. canada and members of both typhus and spotted fever groups of rickettsia are indicated by complement-fixation and microagglutination tests. The study also showed the microagglutination test to be a valuable tool in epidemiological studies.