In order to study cell activation in peripheral blood on bronchial allergen provocation up to 24 h, we investigated 32 asthmatic children, sensitive to house-dust mites. Six healthy young adult volunteers served as controls. Lymphocyte subsets (CD3, CD19, CD4, CD8) and activation markers (CD25-T, HLADR-T, CD23) in peripheral blood as well as soluble IL2-R and soluble ICAM-1 in serum were evaluated. In terms of clinical reaction, 23 children exhibited a DAR, 6 an EAR, 6 a LAR and 3 children did not show a bronchoconstrictor response to allergen challenge with house-dust mite extract (NAR). In comparison to controls, asthmatic children showed a significantly higher expression of CD23 on B-lymphocytes (p < 0.05). Other subsets were in the same range in both groups. After provocation there was a significant increase of CD4/CD8-ratio only in asthmatic children. Serum levels of sIL2-R were significantly higher in asthmatic children compared to controls at baseline as well as at 12 and 24 h after provocation, without variation during observation period. No differences were noted for sICAM-1. Our results confirm the hypothesis that lymphocytes, as important cells in regulation of allergic immune response, are recruited into peripheral blood under allergen challenge conditions in sensitized asthmatic children.