This paper has been written with the intention of illustrating the application of psychoanalytic principles to the treatment of in-patient psychotics by reporting the treatment of a female manic-depressive patient by psychoanalysis at the Cassel Hospital during 1936–38. Unfortunately no reports of intensive in-patient psychotherapy of psychoses in this country have been published. Little prolonged intensive psychotherapy of psychoses has been carried out in hospitals, apart from the Cassel Hospital, where for many years the staff was sufficiently numerous to allow most patients to have daily interviews of significant length. In the United States experimentation has been much more active. Recently Fromm-Reichmann (1947) has reviewed many of the problems encountered in the several Mental Hospitals where psychoanalytic methods of treatment are actively pursued. Rosen has reported daring and courageous experiments. He has reported (1946) the treatment of acute catatonic excitements by psychoanalysis—his chief innovation being the long interview. With one patient the first interview was 16 hours with a break of half an hour. He has reported (1947) favourable results from treating 38 male and female schizophrenic patients, the ages of the patients ranging from 15–49, the duration of illness before treatment ranging from 1 month to 27 years, and the duration of hospital residence ranging up to 11 years. The average daily hours of treatment ranged from 1 to 12, and the duration of treatment ranged from 3 days to 11 months. In my opinion the New York Psychiatric Institute which encouraged Rosen's experiments has fostered a technique about which much more will be heard.