A tolerance for marker residue of fenprostalene in cattle is not needed. The safe concentrations for the total residues of fenprostalene in the uncooked edible tissues of cattle are 10 parts per billion in muscle, 20 parts per billion in liver, 30 parts per billion in kidney, 40 parts per billion in fat, and 100 parts per billion in the injection site. As used in this section ``tolerance'' refers to a concentration of a marker residue in the target tissue selected to monitor for total residues of the drug in the target animal, and ``safe concentrations'' refer to the concentrations of total residues considered safe in edible tissues. [49 FR 26716, June 29, 1984]