As a simple and rapid method for serum lipase determination, assessment was made of electrochemical detection in flow injection analysis (FIA), by measuring the voltammetric prepeak accompanied by the reduction of 2-methyl-1,4-naphthoquinone (vitamin K-3, VK3) due to the effect of free fatty acids. A sample containing lipase was incubated with olive oil as the substrate at 37 degrees C for 10 min to bring about the release of fatty acids. The sample solution was prepared by dissolving the oily residue extracted by ether in ethanol solution containing 3 mM VK3 and 38 mM LiClO4. A 5 mu l aliquot of the sample solution was injected into the flow injection (FI) system. The peak height of the flow signal was linear to lipase activity between 10 and 1000 U l(-1) and RSD was 1.2% for 70 U l(-1) (n = 5). By this method, as many as 30 samples h(-1) can be processed, thus showing this method to be useful and highly efficient.