Sarcoidosis is a multisystem, granulomatous inflammatory disease of unknown etiology. Hereditary susceptibility to sarcoidosis is suggested by reports of familial clustering and a higher prevalence in certain ethnic groups, particularly African-Americans. Over four hundred kindreds been reported in the medical literature and these investigators have recently described 101 families and shown that African Americans have a higher prevalence rate of familial sarcoidosis than Caucasians (19 percent vs. 5 percent). The reasons why sarcoidosis clusters in families or the role of genetic factors in this disease are not known.