ACYL-SUBSTITUTED-INSULINS, PARTICULARLY PHENYL- AND SUBSTITUTED-PEHNYLGLYCYL-INSULINS, ESPECIALLY N-PHENYLGLYCYLINSULIN, N-P-METHYLPHENYLGLYCYL-INSULIN AND N-P-CHLOROPHENYLGLYCYL-INSULIN (1), ARE PREPARED BY TREATING INSULIN WITH AN ACYLATING AGENT, ESPECIALLY THE CORRESPONDING NCHLOROFORMYL-N-PHENYL OR SUBSTITUTED-PHENYLGLYCIN (II). THE NEW COMPOUNDS (I) HAVE HYPOGLYCEMIC ACTIVITY AND ARE USEFUL TO TREAT DIABETES, ESPECIALLY IN SUBJECTS WHO ARE INSULIN FAST.