The synthesis of fatty esters in aqueous medium by alcoholysis; catalysed by lipase from Candida parapsilosis (EC.3.1.1.3) is described. The transesterification of rapeseed ail with methanal leads to an equilibrium state after eight hours, with a yield (methyl esters formed/total fatty acids initially present in the acylglycerols) of at least 53% (73, 45, 65% of the linolenic, linoleic and oleic acids respectively). Yield was already about 42% after four hours of catalysis. This transesterification was permitted by methanol inhibition of hydrolysis of the esters.