The genetic basis of various subtypes of the affective disorders has been investigated by family, twin, and adoption studies, as well as by segregation and linkage analysis. Linkage analyses of bipolar disorder with the chromosome 11p15 DNA markers HRAS1 and INS, and the chromosome Xq28 markers for color blindness and G6PD have been reported. We have used restriction fragment length polymorphisms as markers to examine linkage in three extended families with unipolar affective illness, ascertained through probands with either recurrent unipolar or bipolar II illness. Using an inclusive definition of the affected phenotype, linkage could be excluded up to 28cM around the HRAS1-INS linkage group on chromosome 11p15, and up to 5 cM around the DNA marker DXS52 on Xq28. Negative linkage results were also obtained for two more restrictive definitions of affective illness. Thus, we find no evidence for the involvement of the chromosomal regions 11p15 and Xq28 with unipolar affective disorder in these three families.