The medical records of 974 asthmatic children aged 1-14 years (mean 8.7 +/- 3.9 years) who had been evaluated with skin prick tests (SPT) in two referral Children's Hospitals in Athens from 1975 to 1987 were analyzed. The children were grouped according to their residence into groups from urban area (UR), rural area (RU), and coastals (CO). The prevalence of positive SPT and the sensitizing allergens according to the residential area and the family atopic history were considered. It was found that 662/974 (68%) children had positive SPT with 63.6%, 70.7%, and 80.4% in UR, RU, and CO respectively. There was a significant difference in the prevalence of positive SPT between UR and CO. A positive family atopic history was more often accompanied by positive SPT in UR only. Sensitization to grass pollens was noted with higher prevalence in UR. The house dust mite Dermatophagoides pteronyssinus sensitization was more prevalent in CO. Our results support the notion that the environment can influence the prevalence of sensitization to common environmental antigens, the kind of sensitizing allergen, and the expressiveness of the genetic factor with regard to development of atopic asthma.