The present study compared the influence of hyposensitization treatment with a tyrosine adsorbed house dust mite solution (Migen) and an aqueous house dust mite (HDM) solution on the immunological parameters in 41 adult asthma and rhinitis patients. The immunological parameters included total IgE, spec. IgE and spec. IgG antibody determination, circulating immune complexes (CIC), lymphocyte response to Dermatophagoides pteronyssinus and to candidin and streptokinase-streptodornase (SKD). The two groups were compared to a control group of 123 non-allergic subjects. An increase in spec. IgG antibodies was found, with no change in the total and spec. IgE antibodies. The one year hyposensitization treatments had no influence on the appearance and level of CIC. A positive lymphocyte test to HDM antigen was found in 62% of the controls and in 70% of the treated patients. The response was significantly greater in the allergic patients than in the controls. Under the influence of hyposensitization, an early increase of the lymphocyte response to HDM, followed by a decrease, was noticed, whereas the response to candidin and to SKD remained unchanged. The present study demonstrated that the tyrosine adsorbed HDM extract had the same immunological consequences as the aqueous solution.