It is possible to show by mathematical models that sterilization of males is ultimately more efficient than killing as a method of controlling insects and perhaps other pests. The reason is that although both dead and sterile males fail to reproduce, some portion of the sterile ones will effectively prevent the reproduction of females that were not directly affected by the sterilizing agent. An effort is being made now to broaden the method so that sterilization can be produced by a chemical rather than by radiation. A chemical used in this way is called a chemosterilant. The chemicals that have already shown significant value in laboratory tests fall into three classes: alkylating agents, antimetabolites, and miscellaneous compounds. So far, the most promising compounds are alkylating agents. For this reason, this abstract is confined to the toxicology of these compounds.(Portions of this document are not fully legible)