The aim of this study was to determine the aeroallergen sensitivity of allergic rhinitis patients. A total of 100 cases (female: 59, male: 41, aged between 10-59 years, mean age 27.9 years) who were diagnosed with allergic rhinitis by history and clinical presentation, underwent a prick skin test with 30 aeroallergens, and the important sensitizing allergens were assessed. Skin test reactivity showing > or = 3 mm wheal with erythema as the positive skin test, was recorded. The results of patients with positive skin tests follow. TREES: acacia 19%, mango 16%, coconut 12%. GRASSES: bermuda 17%, johnson 21%, timothy 16%, bahia 16% orchard 18%. WEEDS: pigweed 16%, kochia 14%. MOLDS: alternaria 11%, cladosporium 11%, aspergillus 12%, penicillium 16%, helminthosporium 16%, botrytis 15%, rhodotorula 20%, fusarium 26%, curvularia 26%, smut mix 11%, rust 9%. EPIDERMALS: cat 29%, dog 28%, feathers 37%. INDOOR ALLERGENS: house dust 72%, D. pteronyssinus 76%, D. farinae 79%, American cockroach 60%, German cockroach 41%, kapok 30%. Eighty-five percent of patients sensitive to house dust mites were positive to both D. pteronyssinus and D. farinae, indicating substantial cross-reactivity. The study shows that the house dust mite and the cockroach are important aeroallergen sensitizers among the Thai population, since more than half the patients were skin-test positive to the house dust mite and the cockroach.