Piperazine salts such as the citrate3 are now recognized therapeutic agents for use in human infections with the pinworm Enterobius vermicularis, (Mouriquand, Roman and Coisnard, 1951; Turpin, Cavier and Savaton-Pillet, 1952; White and Standen, 1953; Brown, Chan and Hussey, 1954; Bumbalo, Gustina and Oleksiak, 1954) and the roundworm Ascaris lumbricoides, (Fayard, 1949; Mouriquand et al, 1951; Brown and Sterman, 1954; Goodwin and Standen, 1954). Various piperazine salts have also been found to be effective against Syphacia obvelata, Aspiculuris tetraptera, (Mouriquand et al, 1951; Standen, 1953; Brown, Chan and Hussey, 1954) and Trichinella spiralis, (Chan and Brown, 1954) in the mouse, and against some of the intestinal parasitic helminths of a variety of domestic and wild animals (Mouriquand et al, 1951; Sloan, Kingsbury and Jolly, 1954). We wish to report the results of experiments in which piperazine citrate was fed to cats and dogs naturally infected with a variety of intestinal helminths.