Antibodies to the 3 strains of chlamydia were measured in the sera of 197 subjects; 122 with asthma-related symptoms and 75 from the general population. The subjects underwent a structured interview, spirometry, a methacholine provocation test and skin-prick tests. For chlamydia antibodies, IgG titer values of > or = 1:512 and/or IgM > or = 1:16 were regarded as evidence of a current or recent infection while IgG levels < 1:512 and > 1:32 were regarded as indicative of a previous infection. For Chlamydia pneumoniae, a relationship was found between current or recent infection and wheezing (odds ratio (OR) 6.0, confidence intervals (CI) 1.3-28) and also between IgA antibodies and bronchial hyperresponsiveness (BHR) (OR 3.3, CI 1.3-8.3). For Chlamydia trachomatis, serological signs of a previous infection were found significantly more often in subjects who reported having had asthma at some time: (OR 3.2, CI 1.4-7.1), asthma during the last year (OR 3.2, CI 1.4-7.1), wheezing during the last year (OR 4.2, CI 1.6-6.6) and in those who had BHR (OR 2.7, CI 1.2-6.1). We conclude that a relationship may exist between Chlamydia pneumoniae and Chlamydia trachomatis infections and asthma-related symptoms and BHR.