Advances in the diagnosis of infections by arboviruses derive, in great part, from the expansion of the use of cell cultures as a means of isolation of virus from the patient’s blood and as a method for conducting neutralization tests. In the latter there has been an increase in the trend to use serum in dilutions and constant amounts of virus. Antigens for in vitro tests have been prepared from cell culture fluids and from ascites from mice inoculated with certain arboviruses. New procedures applied to preparation of hemagglutination-inhibition antigens include sonication and trypsin treatment. The use of ascitic fluids from vaccinated mice has made possible the preparation of large volumes of immune reference diagnostic reagents with titers and specificities similar to those of mouse sera. Polyvalent fluids prepared by vaccination of a mouse with several viruses has facilitated diagnoses. Methods applied with increasing frequency in the diagnosis of infections by these viruses are the kinetic hemagglutination-inhibition, agar gel diffusion and precipitation, immunoelectrophoresis, and immunofluorescence tests.