AbstractCatalytic reductive dehalogenation of 5‐bromo‐6‐azauracil with carrier‐free tritium led to 6‐azauracil‐5‐3H of a molar activity of 19.0 Ci/mmole. The reaction conditions for the catalytic reductive dehalogenation were examined in tracer experiments. Microbial transformation was used for the preparation of 6‐azauridine‐5‐3H from 6‐azauracil‐5‐3H. 6‐Azauridine‐5‐3‐ H was prepared at a molar activity of 18.8 Ci/mmole. In both compounds the stability of tritium was investiga