The pathogens that were identified on cultures of material obtained by swabbing of the superficial aspect of the wound and needle biopsy were compared with those that were isolated from material that was obtained at debridement from sixty patients who had post-traumatic or postoperative osteomyelitis. The cultures of material that was obtained by superficial swabbing of the wound and needle biopsy were inadequate for prediction of the presence of aerobic organisms. Moreover, the failure to isolate anaerobes from the material obtained by needle biopsy did not rule out the presence of anaerobic organisms. Therefore, tissue for culture of aerobic and anaerobic organisms must be obtained during operative debridement in order to identify all pathogenic organisms. Fungi were isolated from the material obtained by biopsy in two patients. In addition, histological examination of the tissue obtained at biopsy led to the diagnosis of epidermoid carcinoma in two patients in whom this diagnosis had not been suspected before biopsy. Cultures were negative for mycobacteria in all patients. An additional ten patients who had a tibial non-union and latent osteomyelitis were studied. In nine of them, cultures of material obtained by needle biopsy showed no growth. Six of these nine patients had an exacerbation of the osteomyelitis after intramedullary nailing for the non-union. Therefore, the absence of growth of organisms from tissue obtained at needle biopsy does not rule out the possibility that osteomyelitis may be reactivated after intramedullary nailing with reaming.