BACKGROUND In the period between July, 1992, and July, 1994, 1,159 patients in our Allergy Clinic tested positive to one or more inhalants. The nationalities of the population tested included 806 Saudi Arabs and 241 Western expatriates (mainly North Americans). The others were of various different nationalities. OBJECTIVE Our objective was to determine the pattern of immediate type hypersensitivity reactions among the atopic population in the Eastern Province of the Kingdom of Saudi Arabia. METHODS A standard prick skin test was applied and the reaction was considered positive if there was a 3-mm wheal associated with 10 mm of erythema, greater than the negative control. RESULTS The ten most common reactions in the Saudi Arab patients were as follows: Chenopodium album 53%, Kochia 51%, mesquite 46%, cottonwood 38%, alfalfa 36%, dust mite-farinae 36%, cockroach 35%, house dust 31%, Bermuda grass 29%, and acacia 29%. For North American expatriates living in the area, the ten most common reactions were: dust mite-farinae 43%, house dust 41%, Alternaria 36%, grass mix 34%, Bermuda grass 33%, mesquite 32%, cat 31%, Kochia 28%, alfalfa 24%, and Chenopodium album 24%. CONCLUSIONS Hypersensitivity to pollens, house dust, dust mite and cockroach was common. Mold and cat allergies were only common among Western expatriates.