To the Editor: —The recent Chicago case in which the identification tags of two infants were mixed again makes one inquire what methods are available at present for determining paternity or nonpaternity. As for the determination of paternity, the courts still permit the use of the ancient and notoriously unreliable method of demonstrating similarity of the features of the putative father and the child. In only rare instances is this method justified, however, as when a white woman gives rise to a colored child and the putative father is colored, or when the child and putative father both have six fingers on each hand. The inheritance of certain physiologic traits may be made use of to prove nonpaternity in certain cases. In order to be applicable in medicolegal cases, such traits must fulfil three requirements: (1) they must be so sharply defined that all qualified observers will reach the same