Organomercurials, which were generated by intra-and inter-molecular mercury(II)-promoted electrophilic additions, have been reductively demercurated in situ efficiently using sodium borohydride in the presence of triethylborane at low temperature. Under these conditions, the frequently accompanying side reactions such as reductive elimination and oxidative demercuration have not been detected. (C) 1997 Elsevier Science Ltd. All rights reserved.