The behavior of the 5-phenylhydantoin (5-phenyl-2, 4-imidazolidinedione) ring in the aminomethylation reaction was studied in order to determine the orientation of this substitution. In case of monoaminomethylation, 3-morpholinomethyl-5-phenylhydantoin (or 3-piperidinomethyl-5- phenylhydantoin) was synthesized by the condensation of 5-phenylhydantoin with one mole of morpholine (or piperidine) and one mole of formaldehyde. 1, 3-Dimorpholinomethyl- 5-phenylhydantoin was obtained in the attempted condensation of 5-phenylhydantoin with two moles of morpholine and two moles of formaldehyde. Despite the close resemblance to morpholine the attempted condensation of 5-phenylhydantoin with piperidine and formaldehyde under reflux gave no expected 1, 3-dipiperidinomethyl -5-phenylhydantoin. In case of diaminomethylation using piperidine and formaldehyde, only 3, 5-dipiperidinomethyl-5-phenylhydantoin was formed.