The spermicidal powers of the various chemical contraceptives sold to the public have never previously been compared, and no one has been in a position to say that one spermicide is preferable to another. The only literature on the subject consists of the pamphlets issued by the makers of the different pessaries, and these give little or no information on the length of time taken to kill sperms at stated concentrations. The Birth Control Investigation Committee therefore asked me to undertake this investigation. The work was financed by the Committee, and carried out, with Prof. Goodrich's permission, in the Department of Zoology and Comparative Anatomy at Oxford.