Treatment of mice with slime-extract (SE) from Pseudomonas aeruginosa strain 219 failed to increase the proportion of ingested cells of Salmonella typhimurium by immune macrophages (M phi) of mice. However, activated with SE peritoneal SE peritoneal M phi displayed the enhancement of their nonspecific bactericidal activity. It has been found that immune M phi, depending on the dose of SE used for vaccination, killed intracellularly 38 to 67% of bacterial cells, whereas the mean value for the bactericidal capacity of normal resident phagocytes was 7%. The dose of 100 micrograms of SE enhanced activation of M phi to higher degree than 200 or 400 micrograms. The increase of microbicidal properties of M phi was also seen when mice were pretreated with 50 or 100 micrograms of SE and 24 h later were injected with live S. typhimurium cells. However, the amount of 200 or 400 micrograms significantly reduced the killing activity of M phi against these bacteria.