1. Forty-one cases of which depression was an outstanding symptom have been treated with hematoporphyrin, with laboratory controls. All the cases were under hospital care; by far the majority of long standing; and many had had previous courses of treatment of various types without any improvement.2. Of this series 14 were manic-depressives of the depressed type, 1 manic-depressive mixed, 11 involutional melancholias, 9 schizophrenics, 3 psychoneurotics and 3 miscellaneous with some organic factors.3. Six of the manic-depressives, 1 schizophrenic and 1 psychoneurotic recovered or were much improved; of the balance 10 were improved, 5 showed slight improvement, and 18 were unaffected.4. In all cases improved and unaffected, the blood calcium level and the blood sugar level fell, though all these occurred to a more marked degree in the former group. The sugar tolerance curves fell in the improved group and to a less degree in some of the unimproved cases, though it remained constant or even rose in some of the latter. The improved cases showed a slight loss of weight or at most a very slight gain, while in the unimproved cases the weight in general definitely increased. The basal metabolic rate increased slightly in the improved cases, but in the majority of all cases was within normal limits. The N. P. N. increased very slightly in the cases which did not improve, but fell correspondingly little in those cases which recovered or were improved. There was a general tendency in all cases to a decreased white blood count. In the improved cases the red counts increased, while it fell in the group which remained stationary; the hemoglobin value was unchanged in the former and fell in the latter.Abstract Teaser