A quick, simple and economical biostrip technology was developed for estimation of lactose by immobilizing galactosidase, galactose oxidase and horseradish peroxidase on to a polymeric support. The biostrip is dipped in milk or milk products and, from the colour that develops from an added chromogen, the concentration of lactose can be estimated from <20 to 100+g l(-1). The biostrips may be used in dairy industries, hospitals and remote areas where expensive instruments are not available.