We describe an 11-year experience with bacteremia in a two-physician suburban private pediatric practice. Patients studied were ages 3 to 24 months with a body temperature of greater than or equal to 39.4 degrees C and nonfocal illness. During these 11 years, 23 such babies had bacteremia, 21 with Streptococcus pneumoniae. Three risk factors for bacteremia were identified: absolute neutrophil counts greater than or equal to 10,500/microliters; cool season (November to April), and Yale observation score greater than 10. The positive predictive values for bacteremia were 33, 41 and 57%, respectively, when (1) absolute neutrophil count was greater than or equal to 10,500, (2) absolute neutrophil count was greater than or equal to 10,500 and it was the cool season, and (3) all 3 risk factors existed. Of 158 babies at low risk for bacteremia by these criteria, none was treated and none developed serious complications of bacteremia. Eight of the 23 bacteremic infants received no expectant antibiotic therapy and 15 received presumptive amoxicillin treatment in dosages ranging from 20 to 174 mg/kg/day. Twelve bacteremic infants either were not treated or received dosages of 100 mg/kg/day or less; complications developed in 5 of the 12 (persistent bacteremia, 2; facial cellulitis, 3). The remaining 11 bacteremic babies received approximately 150 mg/kg/day (range, 136 to 174) and none had complications (P = 0.03 by Fisher's exact test). The costs of identifying and treating infants suspected of having possible occult bacteremia were examined.