Flow injection analysis with electrochemical detection was used for lipase assay in pharmaceutical preparations. The method is based on the fact that the current of voltammetric prepeak, accompanied by the reduction of 2-methyl-1,4-naphthoquinone (vitamin K-3, VK3) due to the effects of fatty acids, is proportional to the acid concentration. A sample solution containing lipase was incubated with olive oil (substrate) at 37 degrees C with stirring for 15 min, and the released fatty acids were extracted by ether. No emulsifying agent was needed in the incubation of the enzyme reaction mixture. An acid test solution prepared by dissolving the extracts in ethanol containing 3 mM VK3 and 38 mM LiClO4 (the same composition as the carrier solution) was injected into the flow injection system. The flow signal was linear to the lipase activity ranging from 10 to 1500 U/l for sample solutions obtained from the digestive preparations. By this method, analysis of the fat digestive power of the commercially available preparations could be accomplished with good results, thus showing this method to be practically useful.