Conventional biochemical characterization system of pathogenic bacteria spent too much time to identify pathogens. However, the introduction of new genetic technique has pushed these classical methods aside and rapid determination of pathogenic bacteria in infectious disease become possible. Quantitative DNA/DNA hybridization, Specific DNA probe, and PCR techniques are developed for the identification and detection of almost all medically important pathogens. This development was mainly brought by the accumulation of 16S rRNA sequences of bacteria. From conserved area of 16S rRNA and 18S rRNA sequence, universal PCR primers are designed and universal bacterial and fungal detection system are applied for the rapid diagnosis of causative agent of sepsis and meningitis.