The Kveim reaction was studied in vivo in 50 patients with sarcoidosis. Commonwealth Serum Laboratories Kveim material and a new Danish Kveim material gave 14 and 8 positive reactions respectively, as well as 6 and 8 equivocal reactions. Forty-six of the patients were also tested in vitro for cell mediated immunity to the Danish Kveim material, using both the leucocyte migration agarose technique and the capillary technique. No significant migration inhibition or stimulation were found. A tuberculin skin test was performed in 49 of the patients, and in 45 a dinitrochlorobenzene sensitivity titer was determined. Both tests revealed a depression of the cell mediated immunity. The serum levels of immunoglobulins IgG, IgA, IgM, IgD, and IgE were determined. The serum of each patient was also examined to determine if organ-non-specific and granulocyte-specific antinuclear factors of IgG class, antibodies against native DNA, rheumatoid factor, mitochondrial antibodies, antibodies against thyroid cytoplasm, and parietal cell antibodies were present. IgG levels were above normal in 28 patients; IgE was above normal in 10 patients, 4 of whom were atopics or had an atopic disposition. Organ-non-specific antinuclear factors were present in 17 patients.