Antinuclear antibodies were detected and studied by indirect immunofluorescence in the sera of patients with insulin-dependent diabetes mellitus (IDDM) subjected to allotransplantation of pancreatic islet cell culture (PICT). Continuous cell lines L-41 (derivative of J-96) and HEp-2, a sensitive substrate for the detection of antinuclear antibodies, were used after enzyme treatment. Antinuclear antibodies were detected in 19.0% of diabetics in comparison with 1.5% in healthy volunteers.PICT evidently did not influence these antibodies, although a rise of hemagglutinins against sheep red cells after PICT was previously observed. The data indicate that the nuclear antigens of HEp-2 and L-41 against which antinuclear antibodies are directed are different from those found in human fetal pancreatic islet cells which have been implanted. A possible NAg maturity deficiency in fetal tissue may be another cause of their failure to affect the antinuclear antibodies.