A semiquantitative culture technique for early detection of surgical wound infection was done by rolling a segment of a plastic intravenous catheter across a blood agar plate after insertion into the most inflamed part of the wound on postoperative day 3. Patients were monitored daily for purulent discharge until healing. Of the 53 wounds studied, 44 (83%) had no growth or low-density superficial colonization on the blood agar (generally less than 15 colony-forming units and within the upper 1.5 cm of the catheter). None of these 44 wounds was subsequently infected; therefore, these colonies represented colonization. Of the 9 wounds (17%) that yielded greater than 15 colony-forming units and a diffuse subcutaneous pattern (colonies below the upper 1.5 cm of the catheter), all developed purulent discharge with a positive culture of the same organisms found by semiquantitative culture. This result differed significantly (P less than .01) from the 44 wounds without subsequent infection. This semiquantitative technique has the potential to distinguish infection from colonization and may be useful in diagnosing surgical wound infection.