Groups of children with wheezing during respiratory illness, children without wheezing during respiratory illness, and appropriately matched healthy children were tested for the presence and concentration of leukotriene C4 (LTC4) in nasopharyngeal secretions, employing the techniques of reverse-phase high-pressure liquid chromatography and radioimmunoassay. Although most wheezing children had LTC4 in nasopharyngeal secretions, the concentration of LTC4 among wheezing children who shed respiratory viruses was found to be consistently elevated (mean 1520 +/- 228 pg/0.1 mL) compared with values in wheezing children without evidence of viral infection (mean 709 +/- 147 pg/0.1 mL). In sharp contrast, little or no LTC4 activity was detected in healthy children (mean 106 +/- 77 pg/0.1 mL). These observations suggest that respiratory viruses are stimuli for the release of mediators of inflammation such as LTC4. Thus development of virus-induced bronchospasm may be related in part to direct mucosal cell-virus interaction and the release of pharmacologically active mediators in the respiratory tract.