A blood culture technique that utilized small arterial blood samples or peripheral capillary blood was tested in beagle dogs and pig-tailed macaque monkeys. A bolus of 2.0 × 107 Escherichia coli (ATCC 25922) was injected intravenously into five animals of each species. Blood samples were taken before injection of the organisms and 10, 15, 20, 30, 60, and 120 min after injection. Arterial blood samples (2.0 and 0.2 ml) and peripheral capillary samples (0.14 ml) were taken at each sampling time. Pour plates were prepared from arterial blood for colony counts. All three blood sampling methods were equally effective in detecting sepsis when 10 or more organisms per ml of blood were present. Below this level, the 2.0-ml sample was more effective. Contamination of the peripheral sample with air or skin contaminants was a problem.