Occult bacteremia precedes many serious infections in children. The vast majority of patients with occult bacteremia have an elevated temperature (> or = 39 degrees C), but fever is an extraordinarily common presenting complaint in the 3- to 36-month-old age group, which is at highest risk for S pneumoniae, H influenzae type b, and N meningitidis bacteremia. On examination, most patients with bacteremia will have no findings that distinguish them from nonbacteremic children. A white blood cell count of > 15,000/microL in a child with fever will identify about two thirds of children with occult bacteremia. Blood culture remains the most definitive test. It is important to establish a rational strategy to identify and treat these children before significant sequelae occur.