The dopamine beta-hydroxylase (DBH) gene is a candidate gene in manic depressive illness. DBH is required for conversion of dopamine to norepinephrine, the third step in catecholamine biosynthesis. A few earlier linkage studies have found low to moderately positive lod scores in manic depressive families for ABO which is closely linked to DBH. Based on several studies an association between manic depressive illness and ABO blood type has been suggested. Mutations at the DBH locus might thus be involved in the etiology of manic depressive illness in some families. The DBH gene is reported here as unlikely to be a major gene causing manic depressive illness in a large family. Linkage was excluded assuming a dominant mode of transmission. Several methods were used to minimize misclassification.