In this paper I have attempted to show that serial psychological observations promote a dynamic process in which the relationship to the investigator not only facilitates the collection of data, but also modifies it in the process. The utilization of the awareness of this phenomenon in the interpretation and evaluation of material I have termed the psychological control study. This was applied to the study of correlations of psychological factors in relation to urinary sex hormone output, but has a wider application to psychological research.Psychiatric interviews occurring at times of hormonal pressure brought increased spontaneous production of material, relief of tension and improved social adjustment. In one instance this appeared to be associated with a conversion symptom produced or accentuated by the tension. Repeated observations on these relationships may throw important light on relation of symptoms to hormonal pressure, and have implications or psychotherapy in general.In the present study no correlation could be made between psychological data and 17-ketosteroids because of the flatness of the androgen curve. Although correlations between the psychological picture and minor variations in gonadotropin and estrogen could not be regularly demonstrated, a reflection of the general trends seemed clear, with a definite correspondence at the periods when ovulation was suspected. If Benedek's conclusions are correct, the presence of progesterone, though not demonstrated chemically during the control period, was evidenced in the subject's behavior and productions during the latter half of each cycle.Generalizations on hormonal correlations, of course, cannot be made on the basis of this one observation; it is presented primarily as an illustration of the psychological approach. On the whole, however, it seems to bear out Benedek's contention that sex hormone changes are reflected in psychological productions. Further control studies on urinary hormones are in progress in both men and women, and will be reported in a subsequent communication. From our experience thus far, we believe this approach will prove valuable not only in the field of normal sexual biology, but also in the study of sex variants, neuroses and selected psychosomatic disease pictures.