Anthelmintie studies were systematically carried out on 77 kinds of diphenyl ethers and allied compounds. Of these, the compounds which were able to kill the human ascaris-removed by santonin-within one hour by continued immersion in 1 1, 000 dilution of the chemical were 3-hydroxydiphenyl ether (I), 4-hydroxydiphenyl ether (II), 3-hydroxydiphenyl ether carbamide (III), 4, 4'-dimercaptodiphenyl ether (IV), 4-hydroxydiphenylmethane (V), 2-hydroxydipllenylmethane carbamide (VI), 4-hydroxydiphenylmethane carbamide (VII), 2-phenylphenol (VIII), and 2-chloro-4-phenylphenol (IX). The toxicity of I, which was albe to kill ascaris in the shortest period, in mice was slightly weaker than that of hexylresorcinol (HR) but it was more irritant than HR, and its effect on ascaris treatment in man was unreliable. The irritant properties of VIII and IX were about the same as that of HR, and that of II, III, IV, and V was weaker, and VI and VII were non-irritating. Clinical anthelmintie effect of II, III, and VIII was very weak.