Human rabies immunoglobulin assayed by the rapid fluorescent focus inhibition test suppresses active rabies immunization.

The rabies antibody content of each of ten lots of human rabies immunoglobulin was titrated by both the mouse neutralization test and the rapid fluorescent focus inhibition test. The two tests did not give comparable results, the antibody titres obtained by the mouse neutralization test being 1.4-9.6 times higher than those obtained by the rapid fluorescent focus inhibition test. This titre difference was associated with a consistently lower antibody response in human volunteers who had received post-exposure rabies vaccine treatment which included the administration of RIG assayed by the RFFIT.