Cultures of blood drawn through indwelling intravascular venous and arterial cannulas were compared with those of blood drawn simultaneously by percutaneous venipuncture. In 92% of 174 comparisons, the results were identical. Cultures of blood drawn through indwelling intravascular catheters are as reliable as those of percutaneously obtained samples. In addition, the speed, ease, and lack of trauma in obtaining blood for cultures in critically ill patients further recommends this technique. (JAMA 235:1877, 1976)