The study of Puerto Rican children here reported was undertaken in order to observe the roentgenographic appearance of the bones of infants living under the influence of tropical sunlight and to make a comparison between the roentgenographic appearance of the bones of such infants and that of bones of infants living in a temperate climate. During a previous investigation of the control of rickets made in New Haven, Conn., it was found that the bones of a large proportion of young infants living in this temperate climate showed sooner or later, on roentgenographic examination, certain minor changes that were interpreted as evidence of slight rickets. Because such a large proportion of infants in New Haven showed these slight changes, regardless of the fact that most of them had been given what was thought to be an amount of cod liver oil sufficient to prevent rickets, the question arose1 as