As the result of investigation of the urinary steroid patterns in depressive psychosis in previous communication, the author has been able to demonstrate the decreased excretion of total 17-ketosteroid (17-KS) and total 17-hydroxycorticoid (17-OHCS), increased excretion of free 17-OHCS and decreased excretion of conjugated 17-OHCS. Following these results, the ratio of conjugated form/ free form (C/F) and the percentage of conjugated form/total 17-OHCS (C/T%) seem to have very significant changes in comparison with those in the control. In the present study the author investigated 17-OHCS in plasma of depressive psychosis. The plasma specimens were secured from 10 males and 12 females, all healthy persons (in the age range of 18-47 years old and 23 years in average) for controls, and 12 male and 10 female depressives (ranging 22-64 years in age, the average being 41 years). Measurements were taken on total, free and conjugated forms of 17-OHCS by Nelson-Samuel's and Bongiovanni's methods and for the hydrolysis of conjugated form beef-liver β-glucuronidase was employed. The results are as follows: (Every value shows mean and standard deviation. 1. Total 17-OHCS values were 30.77±10.23 γg/dl for controls and 44.34±21.18 γg/dl for depressives, and those of free form were 10.36±5.00 γg/dl in controls and 23.88±11.17 γg/dl in depressives, those of conjugated form were 20.41±10.59 γg/dl in controls and 20.93±11.43 γg/dl for depressives and C/F ratio was 2.35±1.59 in controls and 0.95±0.48 in depressives. 2. In comparison with depressives and controls, the total 17-OHCS was higher than normal value, being significant from the statistical standpoint. The value of free form was about 2 times higher than the normal, showing significant difference between the two. The C/F ratio in depressives, however, was about half of the normal value. 3. In comparing all the depressives with the small groups of 4 reactive and 4 cerebral arteriosclerotic depressives, there could be found not any specific differences among them. 4. In the four cases with improvement after treatment it was found that total 17-OHCS was increased, free form decreased and conjugated form increased. As the result of these changes, C/F ratio was also increased and the corticoid pattern approached the normal value. 5. The decrease in C/F values was characteristic common both to schizophrenia and depressive, but a difference between the two was found in the fact that, whereas the C/F value was decreased due to a decrease in conjugated form in schizophrenia, it was diminished as the result of a marked increase in free form in the depressive. A discussion was made on the meaning of these findings. 6. In the comparative values of 17-OHCS in the blood and urine of 15 cases, measured simultaneously, it was found that the increase of free 17-OHCS in the blood induced an increase of the free 17-OHCS in the urine, thus directly causing the diminution of C/F value. In addition, it was clarified that an increase of total blood 17-0HCS did not necessarily mean its increase in the total urinary content, and also there was no parallel increase in its values of conjugated form in blood and in urine. In order to explain this point, a discussion was made on the role played by the diencephalon, hyophysis and liver function as well as on the pathological factors.