Anti-allergen antibodies were searched for by an Enzyme Immunoassay in the sera obtained from 60 patients with a clinical diagnosis of asthma. Allergic rhinitis was also present in 28 patients. The diagnosis of asthma was based on clinical criteria that include history and clinical evidence of airflow obstruction. Ten potential allergens (Bermuda grass, Olive tree, Parietaria, Alternaria, Cat hair dander, Dog hair dander, Mite DPT, Mugwort, Birch tree and Timothy grass) common to the Mediterranean area, were utilized. Twenty-five of 60 specimens were seropositive. Mite DPT was the allergen identified in 16 of the 25 seropositive specimens. Six of the 25 seropositive specimens reacted with more than one allergen. This may be due to the existence of similar antigenic determinant groups in the allergens used. There was no correlation between the occurrence of rhinitis in addition to asthma on one hand and the identified allergen on the other. Sixteen of the 25 seropositive patients were female. This observation is believed to be related to their occupation. Dog hair dander was identified as the allergen in 1 of the 25 seropositive patients. The low figure obtained was expected because keeping house pets is not a common practice in Lebanon. The 35 seronegative patients may belong to the intrinsic asthma group or the causative allergen in each case was not one of the 10 allergens used in this study. These results indicate that the house dust mite appears to be the most common allergen in the Lebanese asthmatic group studied.