A study was made of microbial contamination of wounds and wound fluid in 114 patients operated upon (clean and conditionally clean operations). Directly before suturing the subcutaneous-fatty cellular tissue no microbes were revealed in 50% of cases, but in 23% of cases potentially pathogenetic microorganisms were isolated. Potential causative agents of purulent infection were revealed in 50% of the patients on the 1st-3rd postoperative days. Suppuration developed in 3 cases only. In a number of cases there were revealed in the wound discharge such microbes which were not detected before the wound was sutured. Sometimes the presence of even numerous potentially-pathogenic microbes in the wound secretion led to no suppuration.