Blood from 28 children hospitalized with symptomatic enterovirus infections was processed by four different methods in an effort to define optimum conditions for detecting viremia. Enteroviremia was demonstrated in 11/28 children. Virus was isolated by method 1 (serum) in 7/11 children and by method 2 (mononuclear leukocytes) in 9/11, but in only 3/10 and 3/11 children by methods 3 and 4 (granulocytes and plasma-mixed leukocytes, respectively). In four children, the only blood isolate was from mononuclear leukocytes, and in two, serum was the only positive blood preparation. This suggests that viremia can be often detected in hospitalized children with enterovirus disease and shows that the methods used for processing blood may significantly influence the isolation rate.