A blood culture system was developed in which a lysing agent (either Tween 20, one of several other polyoxyethylene adducts, digitonin, or Triton X-100) is added to the blood culture medium. Of 33 Triton compounds, 9 lysed human blood, as did 7 of 21 polyoxyethylene compounds and digitonin, all at a concentration of 0.05%. Under the specific test conditions, three of the hemolytic polyoxyethylene compounds and digitonin had no inhibitory effect. All of the Triton compounds had at least some inhibitory effect on the most sensitive of the pathogenic bacteria that were tested, Streptococcus pneumoniae and Neisseria meningitidis. Because of results from previous studies, Triton X-100 was tested further, despite evidence in this study of its inhibition of bacteria. Of the 55 lysing agents tested, digitonin, Triton X-100, Brij 96, and Tween 20 were selected for further testing as additions to conventional culture broth. Comparative culture studies with bacteremic blood from infected rabbits were performed with the conventional blood culture, the Isolator system (Du Pont Co., Wilmington, Del.), and the new lysing medium. The new system has the advantages of lysis filtration and lysis centrifugation without the associated added cost and processing complexity.