Exposure to cockroach has been reported to cause asthma in many parts of the world. Although house-dust-mite is known to be the most important indoor allergen in Turkey, there are few data on the prevalence of allergy t o cockroaches. Therefore, we evaluated the prevalence of cockroach sensitivity in asthmatic TUrkish patients to see whether it is also an important source of asthma in addition to house-dust mites. A total of 206 patients demonstrating the characteristic features of asthma were included in the study. Sixty-three percent of the patients were considered atopic, and 37% were found to be nonatopic by skin prick tests. Mite allergens were the most common cause of indoor allergy (50%), while cockroach sensitivity was detected in 25.7% of all the asthmatics. Among all cockroach-sensitive patients, 70% were also positive for mites. A female predominance was observed in cockroach-sensitive patients, as 44% of atopic women and 34% of atopic men had positive skin tests with cockroach allergen. The average duration of asthma was 7.1+5.6 years in cockroach-sensitive asthmatics, and there was no difference between groups in average duration of asthma (P>0.05). Mild, moderate, and severe asthmatics constituted 73.6%, 20.7%. and 5.7% of the cockroach-sensitive patients, respectively. These data indicate that cockroach is also an important source of domestic infestation n i Tlirkey. Thus, it seems reasonable to suggest the need for cockroach allergen in the routine battery of inhalant skin tests in this geographic location. However, possible cross-reactivity with mites has to be taken into consideration during the clinical evaluation of subjects with cockroach sensitivity, especially in our patient population with such high rates of house-dust-mite allergy.