A lysed-blood culture system that quickly lyses patients' blood near neutrality and is relatively noninjurious to more delicate pathogens such as Haemophilus influenzae and Bacteroides fragilis is reported. The lysing solution includes culture medium, 0.004 M sodium carbonate and bicarbonate, 0.04% Triton X-100,and 0.6% Rhozyme (a mixture of proteases). Most of the pathogens tested multiplied in the lysing solution. The lysed blood normally is immediately filtered. The membrane is transferred to culture broth. The greatest advantage realized from this blood culture technique is separation of pathogens from antibiotics, bactericidal antibodies, complement, opsonins, and phagocytic systems. Another advantage is the concentration of organisms into a small volume of clear medium for faster growth and visualization of growth. It was observed that both gram-negative and -positive organisms were attracted during filtration to the filter material and were not removed from it by backwashing with buffer. Thus, filter membranes with porosities much larger than would nominally be expected to retain bacteria retained all or part of light and heavy Escherichia coli and Staphylococcus aureus suspensions. Advantage may be taken of this phenomenon to use filters with larger pore sizes and avoid filter clogging by poorly lysed specimens. Porr lysis may result from addition of too much blood to the lysing solution, blood with elevated numbers of erythrocytes or leukocytes, or blood from some people whose blood is naturally more resistant to lysis.