The present invention provides a parasiticidal formulation comprising: Fipronil, or a veterinarily acceptable derivative thereof; at least one C1-C6 alcohol co-solvent, wherein the total amount of C1-C6 alcohol is up to 8% by weight of the formulation; at least one organic solvent which is not the C1-C6 alcohol co-solvent; and at least one crystallization inhibitor, wherein the total amount of crystallization inhibitor is from 2 to 20% by weight of the formulation. The formulations of the invention have higher flash points than known parasiticidal formulations comprising Fipronil and therefore provide safer formulations for use in the home, storage, manufacture and distribution.