This paper has discussed some of the latest discoveries in genetics and in endocrinology and their psychiatric significance. We now know Mongolian idiocy is due to an abnormal condition of the 19th alleles and that it may be associated with Klinefelter's syndrome. It seems likely that a whole series of psychiatric conditions will soon be linked up with disorders of the chromosomes. We realize the importance of the sex hormones. Both the androgens and estrogens are composed of numerous different substances. We do not know the potencies of each one of them nor have we adequate knowledge to correctly quantitate some of them. These are only two of many illustrations that might be given. This spectacular breakthrough is just beginning and the next 10 to 20 years will see still greater additions to our knowledge.After this paper was presented, a basic question was raised by two articles(28, 29) in Lancet for July 16, 1960. The first article reported 2 cases of true hermaphroditism. "The basic diploid chromosome number in each is 46 and the sex chromosome constitution is interpreted as XX. In one patient 18.5% of cells had a chromosome count of 47. Despite the presence of a testis in one case and an ovotestis in the other, no Y chromosome was present." The second article reported one case of true hermaphroditism with 46 chromosomes and "the chromosomal constitution was found to be XX, indicating female sex." It cites 2 articles published a few months previously, each of which reported one case of true hermaphroditism with the sex chromosomes being XX. All this material raises a basic question as to whether the Y chromosome is necessary for the presence of a testis or an ovotestis.