Infants hospitalized with respiratory syncytial virus infection were studied to delineate the quantitative shedding patterns and duration of shedding of RSV. Nasal wash specimens collected edaily from 19 infants contained a mean maximal titer of 4.34 log₁₀ 50% tissue culture infective doses per milliliter. On admission, the mean titer was 4.14 log₁₀ TCID₅₀ with no consistent decline until after Day 6. The mean duration of shedding for 23 patients until they were virus negative was 6.7 days with a range of 1 to 21 days. Quantities of RSV shed were significantly greater in infants less than one month of age and in infants with evidence of pulmonary consolidation on chest roentgenogram. Shedding extended for a significantly longer time in infants with lower respiratory tract disease than in those with clinical manifestations limited to the upper respiratory tract.