Abstract: DIF studies on skin biopsy specimens taken from the extensor surface of forearms of 50 patients with PSS and 10 patients with MCTD were carried out. Epidermal nuclear immunoglobulin deposition was observed in 10% of PSS and 60% of MCTD. The immuno-fluorescent epidermal nuclear staining pattern in patients with MCTD were speckled and the majority of the patients with PSS were homogeneous with none of them was speckled. A positive immunoflourescent band form deposition of immunoglobulins was found along the BMZ in 10% of patients with PSS and 30% of patients with MCTD. The authors discussed the findings in detail and concluded as following: 1. When a patient has sclerosing skin changes (or swelling) of the hands, Raynaud's phenomenon, polyarthritis (or arthral-gia) and shows a speckled epidermal nuclear IgG staining in DIF simultaneously, the diagnosis of MCTD can be established. 2. A positive immunoflourescent band test by DIF is not specific for the diagnosis of MCTD and thus cannot be used as a means to difFerentiate MCTD from PSS.