Schizophrenias have a genetical support as it is now proved by the study of twins born from schizophrenic parents and of the adopted children of schizophrenics. The HLA typing brings an additional argument in favour of this hypothesis. After a recall of data concerning the system of tissular histocompatibility, the results are given of the HLA typing of a population of 65 schizophrenics (59 men, 6 women) including 27 hebephrenics and 38 paranoïds. The paranoïd group is clearly individualized from a genetic point of view. If 40% of the schizophrenics carry the A9 antigen versus 21,2% found in the normal population, 47,4 % of the paranoïd schizophrenics present this antigen (X2) = 12,16 p less than 0,001). The association of the two antigens A9 and CW4 is even more significant: 14,3 % of the total schizophrenic population, as opposed to 2,7 % in the normal population (X2) = 13,3 p less than 0,0005). The paranoid group reached a rate of 24,3% (x(2) = 27,3 p less than 0,0005). A subject carrier of both antigens A9 + CW4 has 11,5 times more the risk of being a paranoïd schizophrenic than a subject not possessing these two antigens.