Sodium triethylborohydride turned out to catalyse regioselective hydroboration of aromatic and aliphatic terminal alkynes with pinacolborane. The conditions for this reaction were optimised and applied to synthesis of a group of (E)-1-boryl-2-alkyl-and (E)-1-boryl-2-arylethenes Although, the catalytic activity of NaHBEt3 can be moderate, alkali metal trialkylborohydrides, which are often used as activators of transition-metal-based catalytic systems, can exert direct influence on the hydroboration pathway. It should be emphasised that each their further use in this role should be preceded by careful consideration of possible influence on actual processes under study.