The objective of this study was to investigate how the development of sarcoidosis influences the disease course of mixed connective tissue disease (MCTD). The cellular composition of MCTD-associated sarcoidosis granulomas was evaluated and also the disease-accompanying T-cell activation and alterations of the serum cytokine levels were measured before and after the therapy. The HLA-DR specific alleles were also assessed. We present two cases with MCTD coexisting sarcoidosis. Serum concentrations of Th1 and Th2 cytokines were assessed by ELISA. Peripheral blood CD3+ total T-cell numbers, CD4+ and CD8+ T-cell subset were determined by flow cytometry. Furthermore, hematoxylin-eosin staining and immunhistochemistry were performed for histological assessment. HLA-DR specific alleles were determined by using PCR-SSP. Elevated number of activated T-cells and high Th1 cytokine levels were detected, mainly IFN-gamma and TNF-alpha. Histologically, CD4+ and CD8+ T-cells were present in the sarcoidosis infiltrations. The haplotypes were to some extent dissimilar from the HLA-DR genotype from patients with MCTD, or sarcoidosis alone. Sarcoidosis enhances the activation of MCTD, based on the laboratory and clinical findings. Our results show that the inflammation is mainly in the effector phase, while granuloma formation is characteristic of the resolution phase of the disease. The assessment of the cytokine network in sarcoidosis-associated MCTD enables us to select the most effective, individualized therapy protocol for these patients.