Co-segregation between Darier's disease and manic depressive illness has been reported. A gene causing Darier's disease has recently been mapped to chromosome 12q23-q24.1, and this region may thus be considered a candidate region potentially containing a gene involved in the aetiology of manic depressive illness. At least one possible candidate gene for manic depressive illness, pro-melanin-concentrating hormone, is located on chromosome 12q23-q24. The present study investigated linkage between manic depressive illness and this region on chromosome 12q, using three microsatellite polymorphisms as genetic markers which flank the gene causing Darier's disease. For all dominant models close linkage was excluded. For broader phenotypic models linkage was excluded in the interval between markers, even in one large family alone.