A disk-shaped reagent based on bacterial NADH:FMN-oxidoreductase and luciferase immobilized into a starch gel is developed. The reagent characteristics, such as activity and stability depend on the time of drying, the initial luciferase preparation content, the source of the starch and its gel concentration. The experimental error of bioluminescence determination does not exceed 10-15%. The method of immobilization into gel provides the coimmobilization luciferase and NADH:FMN-oxidoreductase and their substrates. On the basis of these reagents, the multifunctional immobilized biosensor for bioluminescent assay in medicine, ecology and other fields may be developed. (c) 2006 Elsevier Inc. All rights reserved.