Febrile infants less than eight weeks old. Predictors of infection. Febrile infants less than eight weeks old frequently are admitted and receive parenteral antibiotics for treatment of possible sepsis. The authors assess 52 infants less than eight weeks old with a rectal temperature of 38.1 degrees C or higher as having either a readily identifiable focus of infection by physical examination, appearing "toxic" without a focus, or appearing well. The authors screened patients by using white blood cell (WBC) counts, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and chest radiographs in addition to blood, cerebrospinal fluid and urine cultures. The authors found a 9.6% incidence of bacteria in the 52 infants evaluated, with a 4.3% incidence in those febrile infants who appeared well. Five patients had positive blood cultures with Group B B Hemolytic streptococcus (four patients), and Viridans streptococcus (one patient). A clinical assessment of toxicity and a total band count greater than or equal to 0.5 x 10(3) cells/uL together were sensitive indicators of bacteremia, as were toxicity and a positive CRP. A "toxic" appearance, a WBC count greater than or equal to 15 x 10(3) cells/uL and an ESR greater than 30 were specific indicators of bacteria. Based on these data, identification of bacteremia in febrile infants may be possible with clinical assessment and screening laboratory tests. Because of the relatively small sampling size of this study, the authors feel that evaluation of a larger number of patients is warranted to evaluate these sensitivities in a more diffuse patient population. 