This study deals with the use of a membrane reactor for the enzymatic conversion of cassava starch to maltose. The enzymes used were Maltogenase and Promozyme (Novo Nordisk). Maltogenase activity was unaffected after a 5 h incubation period at 65 degrees C, but Promozyme was markedly heat-unstable even at 37 degrees C. Batch hydrolysis of liquefied cassava starch (30% w/w) by Maltogenase and Promozyme resulted in a maximum degree of starch conversion to maltose of 72% (approximate to 254 g dm(-3) maltose). The conversion degree fell by 11% when no debranching enzyme was used. The residence time distribution of the ultrafiltration reactor (UFR) was that of an ideal continuously stirred tank reactor. Rejection of Maltogenase by Carbosep M4 membranes (MWCO : 50 kDa) was not total. The overall enzyme activity loss after a 5 h diafiltration period was 28%, however about half this loss appeared to be due to enzyme denaturation inside the reactor. During saccharification trials conducted in the UFR at a starch concentration of 30% (w/w), severe membrane fouling occurred. The average permeate fluxes obtained were 14 and 23 dm(3) h(-1) m(-2) at constant transmembrane pressures of 100 and 200 kPa respectively. When the reactor was operated at a space-time of 4.2 h, the degree of starch conversion to maltose in the permeate rapidly stabilized around 55-56%.