One hundred ten substituted melamines were tested as chemosterilants against Musca domestica L. Melamines that were sufficiently basic to form stable salts were tested as hydrochlorides. Fifty-five effectively inhibited hatch or pupation. The most effective inhibitors of hatch were tri- to hexasubstituted methylmelamines. Melamines without methyl groups or methylmelamines containing large alkyl, aryl, or other bulky groups were ineffective against males. As a rule, compounds that affected hatch when both sexes were treated were also effective when only males were treated. Melamines that had 2 free amino groups and small cyclic substituents on the 3rd exocyclic nitrogen were generally without effect on hatch, but they inhibited pupation of larvae produced by treated females. The inhibitors of pupation were ineffective in sterilizing males. All compounds were evaluated in 2 diets: sugar and fly food. The effects of the 2 foods and of the 2 forms of the compounds were often large, but only relatively uniform series of results were considered in structure-activity correlations.