During a 3-month period 252 blood cultures were obtained on adult patients seen in our emergency room with fever and chills suggesting bacteremia. 62/252 blood cultures were positive by standard aerobic/anaerobic blood culture techniques. Buffy coat smears were positive in 76% of patients (47/62) when stained with the acridine orange technique and in 52% (32/62) when stained by the Gram method. Acridine orange was thus superior to the Gram stain for the detection of bacteremia (p less than 0.05). Gram-negative organisms were present in 70% of the buffy coat preparation stain by the acridine orange method. Escherichia coli was the most common organism in buffy coat smears and subsequently identified by blood culture. We conclude that acridine orange stained buffy coat smears provide rapid detection of clinically suspected bacteremia in preselected acutely ill adult patients.