Enteroviral infection is a serious health problem in the newborn infant. Approximately 60-70% of infants diagnosed with enteroviral disease within the first 10 days of life acquire their infection by transmission from the mother at the time of delivery. Congenital infection is rare but often fatal. Perinatal transmission of enteroviral infections in newborn nurseries has also been implicated as an important route of spread of the disease in newborn infants and postnatal transmission of enteroviral infections during seasonal peaks of enterovirus activity occurs commonly. Thus, during periods of high prevalence of enterovirus infection in the community, there are many potential sources of infection both during and after discharge from the nursery, including the mother, other family members, and hospital staff. Approximately 75% of cases of neonatal enteroviral disease carry a benign outcome, with diagnosis and symptomatic treatment in non-intensive care unit settings. For the remainder of patients, more serious consequences can result from systemic enteroviral infection, including meningoencephalitis, cardiovascular collapse, myocarditis, or hepatitis. These last two organ-specific complications carry high mortality rates. Historically, symptom management and supportive care have been the rule in the management of these patients. No specific therapeutic intervention is currently available for the management of these gravely ill neonates. The current study will evaluate the antiviral drug pleconaril as a treatment for enterovial sepsis syndrome. This trial is a multi-center, randomized, placebo-controlled study to evaluate the virologic efficacy, safety, and pharmacokinetics of pleconaril in the treatment of severe enteroviral sepsis syndrome. Patients will be randomized 2:1 to drug or placebo. For enrollment into this trial, infants must have evidence of severe hepatic involvement, myocardial involvement, and/or consumptive coagulopathy. Their age must be 15 days or less at the time of the onset of disease symptoms. Enrollment will continue until 45 subjects with confirmed enteroviral disease have been enrolled. The primary objective of this investigation is to determine if administration of pleconaril to critically ill neonates with enteroviral sepsis syndrome results in more rapid clearance of virus from various body sites. Other objectives of this study are to assess the safety and pharmacokinetics of this drug in this patient population. The effects of pleconaril on measures of clinical outcome also will be evaluated. These include the degree of inotropic and blood product support required during the acute illness; duration of hospitalization; the time to resolution of residual organ injury; and short-term (at 2 months of age) and long-term (at 1 year of age) survival. The primary endpoint will be the percentage of patients shedding virus (as detected by viral culture) from the oropharynx (i.e. throat) 5 days after beginning study drug. The secondary endpoints will include: duration (in days) of shedding of virus (as detected by viral culture) from the oropharynx, rectum, urine, and serum; change in baseline laboratory abnormalities [aspartate aminotransferase (AST), alanine aminotransferase (ALT), bilirubin, platelets, creatinine), reflecting either resolution or progression of enteroviral disease; pleconaril pharmacokinetics; safety; duration (in days) of total hospitalization; survival at 2 months of age; time (in days) to resolution of residual organ-related abnormalities following acute disease; and survival at 1 year of age.