Aeroallergens and antigens in sandstorm dust, extracts of which were skin prick test (SPT) positive in allergic patients, were detected by roeket immunoelectrophoresis and ELISA. Fungi and bacteria isolated by agar settle plates and soil dilution and soil washing methods were enumerated and identified. Cat dander. Acacia, Alternaria. Aspergillus. Chenopodium. Ciadosporium, Bermuda grass, Pitheceilobiiim, Prosopis. Rumex, cultivated rye. and Washingtonia palm allergens were detected by both methods. Viable microbes including 1892±325 eolony-forming units (cfu) of bacteria, and 869±75 cfu of fungi were isolated per gram of dust by the soil dilution method. Randomly selected microbial colonies on streaking and subculture were found to consist of between two and seven mixed colonies. Fungi including Alternaria, Aspergiiius, Botrytis, Ciadosporium, Mortierelia, Mucor, Mycelia sterilia, Peniciilium, Pythium, Uiodadium, Verticiliium, and some yeasts were isolated. Actinomyces, Bacillus, Pseudomonas. and mostly coagulase-negative Staphylococcus species were identified, but the bulk of unidentified bacterial isolates were mainly mixed colonies of rods, cocci, coccobacilli. and some filamentous types. Six-hour agar settle-plate counts during sandstorms were 1(X) and 40% higher for bacteria and fungi, respectively, than without sandstorms. The most abundant aeroallergens were those of Acacia, Alternaria, Aspergillus, Bermuda grass, Ciadosporium, cultivated rye, Prosopis, and cat dander. Pithecellobium duke, Rumex crispus, and Washingtonia palm allergens were detectable for the first time in Riyadh. IgE reactivities ofthe dust in man were demonstrated by ELISA using sera from atopic, exposed, and normal subjects. These results indicate that sandstorm dust is a prolific source of potential triggers of allergic and nonallergic respiratory ailments, and the methods mentioned here should be routinely used for quick sampling of the environment.