This is a multicenter consortium genetic epidemiology study. The investigators will accomplish their goal by organizing a 10-site multi-center consortium to recruit an adequate sample of sarcoidosis families for analysis. They plan to use the affected sibling pair linkage analysis to scan the genome for linked chromosomal regions, transmission disequilibrium testing to evaluate candidate genes in those regions with evidence for linkage, and an environmental questionnaire to collect data to test for possible interactions of susceptibility genes with exogenous risk factors. Genotyping and analysis of data are scheduled to begin in July, 2001 with completion of all analysis by April, 2004.