SUMMARYPlatinum-loaded microporous aluminophosphate molecular sieves (Pt-AlP04-5) were synthesized and studied as catalysts for promoting tritium isotope labelling by exchange between tritium gas and aromatic, heteroaromatic and aliphatic hydrocarbons. The presence of the Pt metal considerably enhanced the activation of the tritium gas. Detailed isotope orientation patterns, as determined by 3H nmr spectroscopy, sho,wed that the A1P04-5 component of the catalyst dominated the exchange reactions, bub some influence of the Pt metal was apparent with some substrates.