Fourteen patients suffering from perennial allergic asthma linked to mono-sensitivity to the house dust mite were studied. An initial bronchoalveolar lavage with standard cytology as well as a study of the T lymphocyte subpopulations (CD3, CD4, CD8, Leu 7) and B cells (CD19) was carried out, representing the basal situation. Four weeks later an allergic bronchial provocation test to purified extracts of the house dust mite was performed taking care to monitor the occurrence of any delayed bronchial response (8 out of 14). A second bronchoalveolar lavage was performed 72 hours after the bronchial provocation test. A significant rise of eosinophils in the bronchoalveolar fluid was registered 72 hours after the provocation test; m +/- sem (%): 3.07 +/- 1.31 vs 7.78 +/- 1.22; p less than or equal to 0.005, Student t test for paired series. This large rise in eosinophils was observed independently of the type of response, whether immediate or biphasic. The CD4 lymphocyte subpopulations were significantly decreased after bronchial provocation tests m +/- sem (%) 12.21 +/- 2.79 vs 6.47 +/- 1.62; p less than or equal to 0.05 Student t test for paired series. There was no overall significant difference after the provocation tests in the CD8 lymphocyte subpopulation. However, a remarkable and significant rise was noted in the CD8 populations after bronchial provocation in 6 subjects presenting with an immediate isolated asthmatic reaction; m +/- sem (%) 10.17 +/- 4.01 vs 34 +/- 7.32, p less than 0.05, paired Wilcoxon test.(ABSTRACT TRUNCATED AT 250 WORDS)