An immunoassay utilizing chemiluminescence and paramagnetic particles has been developed for the new fully automated random access LIAISON immunoanalyzer. The LIAISON Ferritin assay is a two-site immunoluminometric one-step assay using two highly specific monoclonal antibodies. A specially designed unique Reagent Integral contains all specific reagents. The cooled reagent compartment guarantees an on-board stability of at least 4 weeks. The assay works with a 2-point calibrated master curve. To perform, the assay, 10 microliters sample is added to 300 microliters tracer and 20 microliters antibody-coated magnetic particles. After 10 min incubation the particles are separated, washed and the chemiluminescent signal is generated. The time to first result is only 15 min. The assay with a unique extended standard range up to 3,000 ng/ml shows no high dose hook effect up to 150,000 ng/ml (spiked sera). The cross-reactivity to human liver ferritin is 100%, to human spleen ferritin 66% and to human heart ferritin 8%. Precision (within-run < 3%; between-run < 5%), linearity, recovery and sensitivity (< 0.2 ng/ml) are excellent. The assay shows a very good correlation to LlA-mat Ferritin (r = 0.994). In summary the LIAISON Ferritin run on the new LIAISON immunoanalyzer and is a very rapid and accurate method rapidly providing reliable results.