The author surveyed 100 manic-depressive patients hospitalised in Talbieh Psychiatric Hospital, Jerusalem, during the years 1949-1958. These 100 patients are divided into 3 categories: 83% Jewish immigrants from Europe and the Americas, 5% from Asia and Africa and 12% Israel born. Seventy percent were long-time immigrants whereas 16% were newcomers.Data were also presented about 745 manic-depressives, who were discharged from psychiatric institutions all over the country during 1957. The incidence of manic-depressive disease was compared with data from the psychiatric literature. The incidence in Israel, according to the number of discharged patients during the year 1957, was 0.4 : 1000, whereas the incidence in the average population on the whole world is 3-4 : 1000. The author presented hypotheses concerning this observation.