Allergen immunotherapy results in a number of changes in clinical and immunological parameters. To study the kinetic influence of immunotherapy on cytokine production, we evaluated the ratios of Th1/Th2 for patients receiving mite-extract immunotherapy with 3-month intervals. Changes in Th1/Th2 ratio were calculated based on the intracellular cytokine and surface CD4 staining of peripheral blood mononuclear cells (PBMC). No significantly different Th1/Th2 ratios were detected after immunotherapy, although ratios were lower for asthmatic children when compared with normal controls. Cytokine production was also determined on supernatants from mite- or mitogen-activated PBMC cells. A significantly increased production of all cytokines was detected from activated PBMC from patients after immunotherapy. Thus hyposensitization with mite extract for 1 year might improve the cytokine production capacity of asthma patients' PBMC.