WE HAVE CONCENTRATED CONSIDERABLE EFFORT ON THE SYNTHESIS OF 15N LABELLED BASES VIA THE NEW AND VERSATILE METHOD. WE HAVE COMPLETED THE SYNTHESIS OF [6,7,9 15N3]ADENINE. TREATMENT OF THE 4,6-DICHLOROPYRIMIDINE WITH 4 EQUIVALENTS OF AMMONIUM HYDROXIDE AFFORDS THE 4,6-DIAMINOPYRIMIDINE IN 90% YIELD. REACTION OF THE LABELED DIAZONIUM SALT, FOLLOWED BY HYDROGENATION OF THE AZO COMPOUND, AFFORDS THE TRIPLY LABELED MATERIAL. ANNULATION WITH FORMIC ACID GIVES THE ADENINE IN NEARLY QUANTITATIVE YIELD.