One reason for the underdiagnosis of bacteremia as an etiology of fever in neutropenic patients might lie in inefficient blood culture techniques. This possibility was investigated in a retrospective study by comparing the efficacies of a manual and an automated blood culture system used to detect bacteremia in such patients. All neutropenic fever episodes accompanying all 93 intensive chemotherapy cycles of 26 consecutive patients with acute myelogenous leukemia (AML) enrolled in Finnish Leukemia Group AML 86 trial and treated in Oulu University Hospital over 3 1/2 years were analyzed. The chemotherapy protocol and the supportive care of the patients remained the same during the whole period. In 1990-91 the blood cultures were made manually and in 1992-93 with an automated continuous-monitoring culture screening system. Evaluable febrile episodes numbered 53 during 1990-91 and 73 during 1992-93. There was a statistically significant increase (p < 0.05) of culture-positive episodes, from 21% to 40%, when the continuous-monitoring system was adopted. The new method proved to be better than the manual one in detecting bacteremia of neutropenic patients.