Many linkage loci and candidate genes have been reported in molecular genetic studies of bipolar disorder. However, none of these findings have been consistently replicated. Meta-analyses of linkage studies have also reported conflicting results. Among recently reported candidate genes, BDNF, G72, AKT1, GRIN2A, XBP1, GRK3, HTR4, IMPA2 and GABRA1 may have some importance. Study of the possible roles of epigenetics or analysis of genetic diseases, in which bipolar disorder is one of phenotypes, may also be promising. In addition to monoaminergic and intracellular signaling pathways, recent studies have revealed possible roles for mitochondrial dysfunction, for glutamatergic dysfunction and for the endoplasmic reticulum stress pathway.