A batch of antirabies fluorescence conjugate was titrated in five laboratories, with three different makers of microscopes, equipped with a variety of accesories. The titers ranged between < 1:4 and 1:64, depending on the accesories used. The results indicate the need for each laboratory to titrate the conjugate. Also, the disadvantages of distributing the reagent diluted according to the titer obtained by the manufacturer, or mixed with the rabies-infected and normal mouse brain suspensions, are discussed.