The one-step procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixed-bed reactor. Application of supercritical NH3 as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8-10%). The main reason for the low diamine selectivity of 1,3-dihydroxy compounds is water elimination leading to undesired monofunctional products via alpha,beta-unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4-dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3-propanediol.