The authors studied the relationship between dust mite antigen concentrations in house dust samples and the occurrence and frequency of wheezing in 58 children with dust mite allergy (wheal > or = 4 mm. mean diameter in response to a prick test with either D. farinae or D pteronyssinus antigen). According to their parents, 15 subjects had never experienced recurrent wheezing, 8 had a history of past recurrent wheezing but no recent wheezing, and 35 had a history of recent wheezing. Spirometry data were obtained with a water seal spirometer and a limited dose methacholine challenge (total cumulative dose = 6.4 micromoles) was performed. Dust samples were obtained from 6 sites in each home: the child's mattress, blanket, pillow, bedroom floor, and the recreation room couch and floor. Der fI antigen concentrations were assayed using a monoclonal antibody based ELISA and expressed as ng/gm sieved dust. Concentrations of Der fI were > or = 10,000 ng/gm in at least one microenvironment in the bedrooms of 86 percent of subjects. Mean concentrations of mite antigen in different micro-environments did not differ significantly for dust mite allergic children with and without histories of recent wheezing. Among children who had experienced recent wheezing, mean concentrations of mite antigen tended to be higher in dust samples from homes of the 19 children who had experienced > or = 5 episodes of recent wheeze than in samples from the homes of 16 children who had experienced fewer episodes of recent wheezing; however, differences in mean concentrations of Der fI in the microenvironments sampled were not statistically significant. Similarly, Der fI levels in dust samples were not related to spirometry, or to methacholine responsiveness.