One of the most essential procedures in the identification of many Lepidoptera is an examination of the genitalia, and for a most critical examination of these organs slide mounts must be prepared. In many cases, the preparation of slides is one of the most neglected arts in lepidopterology. This is to be deplored, for a well-prepared slide is not only handsome but also much more valuable taxonomically than a messily prepared one. For large and medium-sized specimens, I have found the following technique very gratifying in producing slides of uniformly high quality. Certain phases of the technique are not particularly well adapted for working with smaller moths.