Natural prostaglandins (PG) F2alpha and E1 as well as (+)-cloprostenol were regioselectively 11-acylated using Novozym 435 as a catalyst and vinyl acetate as an acyl donor. Unlike the above compounds the 15-OH group of PGE2 was also acylated with a significant velocity under the same conditions. The enantiospecificity of the lipase-catalysed 11-acetylation of cloprostenol was established by separate treatment of(+)- and (-)-cloprostenols.