The families of 26 married bipolar manic depressives were examined in detail. The rate of affective disorder in their spouses, and the parents and siblings of their spouses, was ascertained. The prevalence of affective disorder among the parents and siblings and of the spouses of age- and social class-matched schizophrenics and well controls was also ascertained. Finally, the prevalence of affective and other psychiatric disorders in the adult offspring of the bipolar probands was ascertained and related to the presence or absence of affective disorder in the spouse. We did not find clear evidence of assortative mating for major affective disorder, although dual mating for affective disorder had the expected result of increasing the risk for affective disorder in the adult offspring.