A composition and method is provided to modify sperm fertility and sex ratio ofmammalian offspring. The composition includes an amount of a class of compoundsof phenoxazine or phenothiazine, having the structure (see FIG. l) and ionicderivatives thereof, wherein R1 is H, a lower alkyl group or N (R3)2, R2 is N, S,O, and R3 is H or a lower alkyl group. A second component of the composition is anamount of an electron transfer agent capable of oxidizing a reduced cofactor(NADPH or NADH). A third component of the composition is an amount of a hexose sugarand/or the phosphorylated esters of such. When mixed with living sperm priorto or at the time of insemination, the composition results in modified rates ofconception and an alteration of birth sex ratio in mammal species.
