The authors present the results they obtained which interspecific cell hybrids. The hexosaminidases A, B and C, seem to be under the control of the two genes alpha and beta, B and CS constituing homopolymers (beta beta)n and (alpha alpha)n, A being a heteropolymer (alpha beta)n. The isozyme CF, particularly abundant in fetal tissues and found also in Tay-Sachs by some authors is, in all probability, under independent genetic control.