Rodenticidal compositions comprising a rodenticidally effective amount of an isomer of a 3-substituted-4-hydroxycoumarin rodenticide which is capable of existing in more than one stable isomeric form. The isomer, for example, the trans isomer of brodifacoum, is significantly less persistently retained in the tissues of non-rodent mammalian or avian species likely to consume the composition or poisoned rodent carcasses than other isomers of the same 3-substituted-4-hydroxycoumarin. The compositins are substantially free of such other isomers, e.g., the cis isomer of brodifacoum, thereby reducing the risk to non-target species from accidental ingestion.
