The relationship between tissue-associated and wound fluid-associated levels of bacteria in closed, healing experimental incisional wounds seeded with Escherichia coli was examined in 200 rats. Tissue specimens and moist swab specimens were taken simultaneously and cultured by a single plate serial dilution method. Colony counts of approximately 105 bacteria/gm of tissue were found to be equivalent to colony counts of 103 bacteria/ml of specimen obtained on a moist swab. Moist swab sampling of an incisional wound therefore offers a direct and simple method of ascertaining infection (defined by others as 105 bacteria/gm of tissue). Moist swab sampling obviates the necessity of surgical manipulation of the patient and subsequent weighing and grinding of tissue in the laboratory.