Universal 16S rRNA gene polymerase chain reaction (PCR) is a promising means of detecting bacteremia. Among other factors, the PCR reagents play a prominent role for obtaining a high sensitivity of detection. The reagents are ideally optimized with respect to the amplifying activity and absence of contaminating DNA. In this study, it was shown in a universal 16S rDNA real-time PCR assay that commercial PCR reagents can vary greatly among each other in these characters. Only 1 of the 5 reagents tested met the criteria of sensitive detection of pathogen DNA with a minimum of false-positive results. The reagent was validated by the detection of pathogens at low titers using bacterial DNA extracted from blood that was spiked with various Gram-positive and Gram-negative bacteria.