Affective disorders are usually referred to as being inherited multifactorially. The contribution of a gene locus in illnesses displaying multifactorial inheritance may be assessed by searching for associations of alleles to the illness. The tyrosine hydroxylase gene encodes the rate-limiting enzyme in the synthesis of catecholamines and might be a candidate for causing the manic-depressive phenotype. Therefore, we tested 88 patients with affective disorders and 99 healthy control persons for association of restriction fragment length polymorphism (RFLP) alleles at the tyrosine hydroxylase locus. The comparison of allele or genotype frequencies did not reveal any significant differences between the two groups.