To know the frequency of positively of several skin tests, data cards from patients, of the Allergy and Clinic Immunology Service of the Hospital de Especialidades del Centro Medico Nacional Siglo XXI (Mexico City), between January, 1989 and March, 1995, were reviewed. Aqueous extracts manufactures by our laboratory were applied, in a dilution of 1:1000 weight-volume. 1091 from 5,651 skin tests patients were positive. Asthma and rhinitis were diagnosed in 492, allergic rhinitis in 289, allergic asthma in 111, and other diagnosis in 199 cases. The most frequent inhalable aeroallergens were house dust and perennial Dermatophagoides p and f1 with predominance in the rainy season, followed by pollens from Fraxinus a. Quercus a and Capriola, with predominance in the rainy season. The most frequent fungi were Candida and Fusarium, with predominance in the dry season.