Based upon the phenomenon that the peptidoglycan, a common component of Gram positive and negative bacteria, reacts specifically with silkworm larvae plasma (SLP), a new laboratory method named “SLP test” was developed to measure the reaction products in plasma quantitatively as SLP. This SLP test seems to be able to diagnose both Gram positive and negative bacterial infection. So we evaluated its usefulness in diagnosing clinical infectious diseases. This study included 14 patients with result to positive bacterial blood culture, 22 patients with bacterial local infection, 7 patients without any evidence of bacterial infection, and 19 healthy volunteers. It seemed that the cut-off value of this SLP test should be set at 0.6 neml. The sensitivity and specificity of this SLP test were 57.1%, 100%, respectively. A significant difference was not detected statistically between SLP values of patients with Gram positive and Gram negative bacterial infectious diseases. So the SLP test did not appeared specific to either Gram positive or Gram negative bacteria. This test may become a new method diagnosing bacterial infectious disease.