A new process for the simultaneous enzymic synthesis and purification of N-(benzyloxycarbonyl)-L-aspartyl-L-phenylalanine methyl ester (ZAPM), a precursor of aspartame, has been developed. The enzymic reaction between N-(benzyloxycarbonyl)-L-aspartic acid (ZA) and L-phenylalanine methyl ester (PM) was carried out in a biphasic hollow-fibre rector with an aqueous phase an a butyl acetate phase. The reaction took place in the aqueous phase and by maintaining the pH at 5, the product (ZAPM) was extracted into the organic phase. Product purity was greater than 90% and reasonable productivity could be achieved with this system.