Bipolar (BP) affective disorder is a severe, heritable condition affecting about one to two percent of the population. The mode of inheritance is poorly understood and probably involves multiple loci of moderate effect. The NIMH-IRP is one of twelve sites participating in a multi-center study concentrating on affected sibling pair families with the overall aim of collecting a large sample of interviews and cell lines from BP families suitable for linkage and association studies. The overall project is funded by an NIMH Extramural Program (MH 59535) grant. The study design uses affected sibling pairs and their family members. DNA and interview data are collected and shared within this consortium of investigators studying BP affective disorder. Cell lines and interview data will eventually be made freely available to the scientific community according to NIMH criteria. The NIMH-IRP site has now enrolled and ascertained a total of over 2000 individuals consisting of BP sibling pairs and their families. (the second highest number among all of the twelve nationwide sites in the Consortium). The initial results from a whole genome screen analysis using the first half of the new data from 250 BP families collected since 1998 was published this year. Two chromosomal regions (one on 17q and one on 6q) had lod scores of 3.63 and 3.61 that met simulation criteria for genome-wide significance. Continuation of this protocol will allow expansion of a sample of affected sibling pairs and their family members. This should add to the likelihood of identifying chromosomal regions and genes relevant to BP and related neuropsychiatric disorders.