In an attempt to define a clinical index for the timing of blood cultures in febrile patients with acute leukemia, subjective symptoms at onset of bacteremia were investigated in a total of 109 consecutive episodes. General malaise, chills, and nausea and vomiting were most frequently observed (66%, 59%, and 50%, respectively). The gastrointestinal (GI) symptoms including nausea and vomiting, abdominal discomfort and fullness, abdominal pain, and diarrhea were encountered in 72% of all the episodes, forming the second largest group next to those closely associated with high fever. These GI symptoms were usually mild and of brief durations, and their occurrence had no relation to sites of infections or etiology of bacteremia. In some cases, nausea and vomiting were aggravated by intensive antileukemic chemotherapy or massive GI bleeding. It was thus suggested that GI symptoms, particularly nausea and vomiting, concomitant with a remarkable, sometimes abrupt rise in temperature during granulocytopenia may serve as a useful index for the timing for blood collection for culture to improve the probability of detection of bacteremia.