Ninety children with bronchial asthma were evaluated for the presence of house dust, house dust mite. Aspergillus fumigatus and milk allergy in vivo by prick test (skin test) and in vitro by RAST. Of the 20 children tested for house dust allergy 12 were positive by skin test and six by RAST. Only six were positive by both methods. Of 25 children tested for house dust mite, 16 were positive by skin test, 13 by RAST and 11 by both methods. Of 35 children tested for aspergillus fumigatus, 25 were positive by skin test, 19 by RAST and 11 were positive by both methods. In the case of 10 children under three years of age with known hypersensitivity to milk, all were negative by prick test and three were moderately positive by RAST method. The correlation of skin test with RAST was 65% for house dust, 72% for house dust mite, 37% for aspergillus fumigatus and 70% for milk. Overall correlation of skin test with RAST was 56·7%.