Local research had shown increased asthma admission rates in the Asian ethnic group in Blackburn, U.K. Patients also reported that asthma seemed to develop some years after first arrival in the U.K. A community prevalence survey of respiratory symptoms and asthma was undertaken in three practices with no special asthma interest. The questionnaire was administered by a Health Visitor and language link worker. Of the Asian patients in the practices, 96.6% were studied. The age distribution was similar to that of the local 1991 census. Of the patients, 181/1783 (10.2%) had diagnosed asthma but positive responses to individual questions suggested underdiagnosis of asthma. Asthma prevalence was higher in males up to age 20 (14.6% vs. 8.2%), and aged over 50 (16.5% vs. 10.5%), but higher in females aged 20-49 (5.6% vs. 9.2%). There were no correlations with social class or Jarman index, and no effect of country of origin or duration in the U.K. by multivariate analysis. The prevalence of diagnosed asthma at ages 5-9 and 10-14 was higher than in previous studies. Diagnosed asthma prevalence rates fell in the 20-49 age band but rose again in the over-50s. In all age groups the prevalence of asthma is probably underestimated. Asthma prevalence was not related to social factors. The data show that those born in the U.K. are more likely to describe regular symptoms and to be on regular treatment, but that for those born abroad there was an increasing rate of symptoms and medication use with increasing duration in the country. These observations confirm patient views but are explained by the age/sex distribution of those born in the U.K. compared to immigrants.