Detection of simian immunodeficiency virus (SIV) antibodies has proved useful in a wide variety of research studies. Conventional immunoassays, however, are difficult to perform outside the well-equipped laboratory or under field conditions. We have developed an inexpensive, simple, rapid immunoassay for the detection of SIV antibodies that utilizes inactivated SIV antigen and Fast-Chek (F-C) (E.Y. Laboratories, San Mateo, Ca)., which is a membrane/filter paper device that uses protein A gold to detect antibody and/or antigen. This low-cost 10-min assay requires minimal technical skill and no refrigeration, electrical power, or sophisticated laboratory equipment. In a study of 155 banked sera, from a number of monkey species in a variety of geographic locations, F-C and Western immunoblot result concordance was 96%. Relative sensitivity and specificity were 98% and 95%, respectively.