The flow injection chemiluminescence (CL) determination of ornithine and the sequential determination of lysine and ornithine by using immobilized lysine oxidase are described. Hydrogen peroxide produced in the enzyme-catalysed reaction is determined by luminol CL. The calibration graph obtained by injecting ornithine solutions into the carrier stream (phosphate buffer, pH 8.0), is linear over the range 1.0x10 - 6 -2.4x10 - 5 M. The detection limit (3σ) for ornithine is 4x10 - 7 M. The sample throughput is 60h - 1 . Sequential determination of lysine and ornithine is based on chemiluminescence measurements on a lysine/ornithine mixture at both pH 6.0 (lysine response only) and 8.0 (lysine and ornithine). Lysine and ornithine can be determined in the range 1.2x10 - 7 -6x10 - 5 M. Relative errors are in the range 3-6%. The interference effects of some amino acids and metal ions are investigated.