"Index Medicus" and 18 other publications have been consulted in an attempt to provide an easily assimilated selection of the recently published and widely dispersed material relevant to the ethical debate the editors of the "BMJ" called for on 4 March 1978. The medical profession is shown to be deeply divided on the ethics of a predictive test for Huntington's chorea. Some members are already using the prospect of a reliable test as an inducement to potential transmitters of this incurable hereditary disease to postpone procreation. Other members would prefer to see any future test withheld from every applicant until such time as radically improved means of treatment or a cure is discovered. The evolution of generally acceptable professional guidelines requires further informed debate.