We analyzed polymorphisms of IL-10 -1082 G/A, IL-18 -137 G/C, TLR4 +896 A/G, and IFNG +874 T/A in 139 infants under 6 months of age hospitalized with bronchiolitis and 400 unselected blood donors. Causative viruses were determined by PCR. Infants with bronchiolitis associated with a virus other than respiratory syncytial virus (N = 18), were more often IL-10 -1082 allele G non-carriers, that is, homozygous for allele A (AA) than controls (66.7% vs. 28.0%, P < 0.0001). Infants with RSV bronchiolitis did not differ from controls. This finding suggests a different pathogenic mechanism for RSV bronchiolitis as compared with wheezing associated with other viral infections, for example, rhinovirus in infants under 6 months of age.