Introduction of microbiologically contaminated materials into mice can cause infections of the recipients and jeopardize experimental protocols. As such, the methods used to screen biological materials should be sensitive, reliable and suitable for routine diagnostic work. In this report, the sensitivity of the viral plaque assay, mouse antibody production test and polymerase chain reaction (PCR) for detection of MHV-A59 and MMVp, two of the most prevalent pathogenic viruses in experimental mouse facilities, was compared. Analysis of serial tenfold dilutions of virus stocks revealed that the sensitivity of the mouse antibody production test on day 28 (10(-10) dilution) was at least 10 times higher than that of the viral plaque assay (10(-9) dilution) and 10(4) times more than that of the RT-PCR (10(-6) dilution) for detection of MHV-A59. For detection of MMVp, the PCR (10(-10) dilution) proved to be 10(6) times more sensitive than the viral plaque assay (10(-4) dilution) and the mouse antibody production test on day 28 (10(-4) dilution) which were equally sensitive. Based on the present study, it was shown that the method for diagnosis of viruses in biological materials should be employed only after the sensitivity has been determined for the viruses of interest implying that the most sensitive method needs to be determined independently for each virus.