Intraperitoneal administration of Proteus vulgaris living culture of various age (12 hrs and one day) caused impairments in lipid metabolism in mice liver, kidney and heart tissues. The one day-old culture was more toxic. The impairment in lipid metabolism was manifested as distinct increase in cholesterol content in liver tissue and kidney and a decrease in phospholipid content in liver, kidney and heart tissues. These changes were accompanied by an increase in content of sialic acids in liver tissue.