Enzymatic synthesis of cefaclor was carried out with kinetic control. The product yield was improved by the continuous removal of product from the reaction mixture via complexation of cefaclor with 1-naphthol. The effects of pH and temperature on the enzymatic and complexing reactions were investigated. The efficiency of the enzymatic conversion of cefaclor in the complexing reaction was 80% under optimum reaction conditions. In situ product removal (ISPR) decreased product concentration in the bioreactor, consequently the yield of cefaclor increased from 57% (without ISPR) to 80% (with ISPR). The specially designed reactor allowed enzymatic reaction and product removal to be accomplished simultaneously, in which the productivity of cefaclor was improved to 65 g dm(-3) by semi-continuous operation lasting for 55 h. (C) 2004 Society of Chemical Industry.