The results of skin prick tests (SPTs) performed between 1981 and 1992 on 7099 adult patients with asthma and/or rhinitis were retrospectively analyzed. Standardized Soluprick extracts of Dermatophagoides pteronyssinus, animals and pollen, and unstandardized extracts of Cladosporium++ and chironomids (red mosquito larvae, Chir), were used. The proportion of atopics (patients with positive SPT results) was 44 percent, decreasing from 61 percent in patients 14-20 years old to 18 percent in patients 61-70 years old. The decrease with age was most pronounced with timothy, cat and horse allergens. In the whole patient group, timothy, cat and birch gave the highest number of positive SPTs. Positive SPTs with dog and Chir were more common in asthmatics than in patients with rhinitis, whereas pollen allergy was more common in patients with rhinitis. Sensitization against D. pteronyssinus, timothy and Chir was more common in men than in women. Of the atopic patients, 65 percent were sensitized against several allergens and 35 percent had a mono-allergy, most frequently to D. pteronyssinus (7.4 percent) and timothy (70 percent). The proportion monoallergies/multi-allergies was higher in older patients than in younger ones. The degree of atopy, expressed as the sum of plusses of the test results with eight allergens for each patient, was higher in younger patients than in older ones. The size of the wheals induced by the positive histamine control increased with age, and the histamine-induced wheals were larger in men than in women and larger in non-atopics than in topics. Strong correlations were found between test results with cat, dog and horse. A greater proportion of the patients with an isolated pollen allergy were born in February-May than was to be expected. The proportion of positive SPTs with mugwort (Artemisia), in relation to positive SPTs with other pollen allergens, decreased from 1981 to 1992. It can be concluded that sensitization to various inhalant allergens is influenced by age, and to a lesser extent by sex, and that pollen sensitization is influenced by the month of birth. During a 12-year period, sensitization to mugwort showed a decrease, as compared to other pollen allergens.