Blood cultures are often essential in the diagnosis and prognosis of disease. Frequently, however, the results obtained are difficult to interpret and correlate with the clinical state of the patient. Limitations and confusions resulting may be attributable to (1) contamination due to faulty technique in the drawing of blood or in laboratory procedures, (2) preconceived ideas of bacterial "nonpathogenicity," and (3) variations in techniques of blood culture. Bacteria can be recovered from the blood stream during physiological states and under all pathological conditions from minimal local infections to septicemias. The significance of an organism recovered from the blood stream lies in its meeting certain basic criteria. This study was made in an attempt to correlate the clinical status and the laboratory findings in patients who have had blood drawn for cultures. Certain criteria to facilitate this correlation were established. Arnold1experimentally produced frank bacteremia in dogs by introducing a