NIH [National Institutes of Health] tests (63) were analyzed. A BPL [.beta.-propiolactone]-inactivated tissue culture rabies vaccine no. 108 was compared with the national standard vaccine A 18 fourteen times in different tests. Reproduction of results is unsatisfactory with the NIH test. This test in its present traditional method with 2 injections is not very suitable for satisfactory potency evaluation of inactivated rabies vaccines. Proposals for modifications are made.