For primary isolation and titration of street strains of the rabies virus from brains of suspected animals, an assay prepared on the cell culture BHK-21/C 13 (rabies infection test - RTCIT) was used. The above assay proved to be reliable and its sensitivity proved to be comparable to the standard mouse inoculation test. Through this test, the results were obtained within 24 to 48 hrs on Lab-Tek tissue culture chamber/slides. It was found out that DEAE-dextran added to the cell culture only slightly increased the invasiveness of the virus in the samples tested. The method described herein is able to substitute the mouse inoculation test (MIT). In our laboratory, 20 vaccination strains of the rabies virus Vnukovo-32/107 and 25 street strains of the rabies virus (delivered from the field) - original fox brain suspensions. And 10 brain suspensions were negative when tested in laboratory conditions (by PMIF, RTCIT as well as by MIT methods).