The crystal structure determinations of over 235 natural and synthetic steroid molecules reported from 1945 to 1974 constitute the most detailed block of structural data on any class of biologically active molecules in existence and provide a wealth of raw material concerning molecular con­ formation and intermolecular interactions ideally suited to the analysis of structure-function correlations. Volumes of physiological data gener­ ated in studies ranging from simple dose-response characterizations to elegant examination of receptor binding sites make up the functional counterpart to this structural data reservoir. The utilization of these data for purposes of exploring biochemical reactions at the molecular level has been inhibited by lack of communication among structural chemists, bio­ chemists, and clinicians. The typical non-crystallographer in the fields of biochemistry and endocrinology finds it difficult to interpret structure reports. The molecular features of key importance from his point of view are often omitted, and, although atomic coordinates are usually tabulated, he may be unable to calculate the details which he needs. Structure reports on steroids have often been published in obscure journals and in some cases the paper has been extremely brief and no mention of the biological importance of the material has been made. Lack of uniformity in presen­ tation of data has also been an impediment to utilization of these data by non-crystallographers. Similarly, the average crystallographer has difficulty assessing data concerning biological activity.