The results of 11 captive matings among nine female and six male descendents of six wild-caught female common garter snakes from polymorphic populations near Lake Erie confirm that melanism is inherited as a simple Mendelian trait and is recessive to a striped pattern. The make-up of litters born to 71 wild-caught females from five sites corroborate this result: striped females never produced all melanistic litters and the frequency of entirely striped, mixed, and entirely melanistic litters conforms to expectations based on estimated allele frequencies. Possible explanations for a previously reported non-Mendelian inheritance of melanism include the occurrence of a somatic mutation or bias in sperm production and fertilization ability.