The methods of synthesis for p-phenylenediguanidine, p-bromophenylguanidine, p-iodophenylguanidine, 4,4'-diguanidobiphenyl, 4,4'diguanidodiphenylmethane, and certain of their salts have been described.2. The effects of p-phenylenediguanidine, 4,4'-diguanidobiphenyl and 4,4'-diguanidodiphenylmethane upon the blood sugar of normal rabbits have been studied and compared directly with the hypoglycemic properties and toxicity of a compound of the synthalin type, 1,6-diguanidohexane, and the results are briefly discussed from the point of view of hypoglycemia and chemical constitution in the guanidine field.