Airborne mold monitoring in three cities in Saudi Arabia has documented the presence of Cladosporium in high concentrations. The spore counts reached threshold levels for sensitization at Jeddah and Al-Khobar with prominent seasonal variations. The concentration in Riyadh (central region) showed levels with minor fluctuationgs and a minor peak towards the month of Novermber. Indoor monitoring also revealed the presence of Cladosporium. Ten species of Cladosporium were idenified with C. sphaerospermum, C. herbarum, C. cladosporoides and C. macrocarpum being most prevalent. The species are relevant in relation to extracts for diagnosis. Skin testing of asthmatic children in Riyadh and Makkah revealed reactivities to Cladosporium extract of 5.8% and 31.3%, respectively. This indicates that Cladosporium may be an important allergen in the region that necessitates further biochemical and immunochemical studies to confirm the allergic impact of the species of Cladosporium prevalent in the region.