A continuous flow bioluminescent method for NADH analysis has been developed using nylon 6 as a solid support. Bacterial luciferase and NAD:FMN oxidoreductase are covalently co-immobilized to a nylon coil (1 m × 1.0 mm ID). The reactor (nylon coil) is placed in front of a photomultiplier tube inside a luminometer linked to an air segmented continuous flow system. Response is linear from 1 to 2500 pmol/tube allowing determination of NADH at picomolar levels. Inter and intra assay precision of the method is satisfactory (5-10%). Range of sample volume injected is 5-100 μl. More than 20 samples per hour can be analyzed and no carryover was observed. The stability of the nylon immobilized enzymes is high (over 2 months) and over 500 samples can be analyzed with a few mg of enzymes.