The cockroach has been reported as a major allergen in inner city asthmatic patients. The retrospective chart review of 799 patients tested over a 10-year period (1981-1991) derived from a private allergy practice and a university allergy clinic is reported. Patients from both groups were divided geographically by home zip codes into inner city, suburban, or rural small town populations. Criteria for positive skin tests were wheal greater than 5 mm for prick and greater than 10 mm for intradermal tests with flare. Overall, 36.9% (295/799) of all patients surveyed were positive by either prick or intradermal skin testing. Cockroach reactivity was observed in 38.6% (95/246) of the private patients tested with 36.2% (200/553) of the university patients showing positive results. The inner city populations in both groups of patients were similar with 43.7% and 40.3% of the private and university patients, respectively, testing positive, with an overall positivity of 41% for all inner city patients. Inner city and rural small town populations for both study groups demonstrated almost identical reactivity with 41% and 43% overall positivity, respectively. Of the suburban group, 37.5% of the private patients and 28.8% of the university patients had reactive skin tests results with an overall rate of positivity of 30.1%. This rate (30.1%) is significantly less than the rate for either inner city (41.0%, P < .05) or rural small town (43.6%, P < .01) populations.(ABSTRACT TRUNCATED AT 250 WORDS)