A microtechnique (modified Takatsy) is described which can be applied to complement fixation, hemagglutination, hemagglutination inhibition and metabolic inhibition tests. The system permits an 8-fold saving of reagents and rapid performance of microdilutions. The specific methods and modifications of equipment necessary to obtain reliable results are presented in detail. Comparative data obtained with the micro- and standard systems establish the reliability and validity of the microsystem.