An interesting association between the sex ratio at birth and the ABO blood group system has been demonstrated by Sanghvi (1951). He showed, in each of two population samples, one from New York and the other from Bombay, that the sex ratio (percentage of males) of Group O infants of Group O mothers was significantly higher than that of Group A infants of Group A mothers ; the ratio for Group B infants of Group B mothers approximated closely with the first ratio. Allan (1952a; 1952b; 1953) further analysed Sanghvi's material and also attempted to correlate the sex ratio data with certain fertility data of various mating types compiled by Waterhouse and Hogben (1947).