The authors describe a bioluminescent immunoassay of LH in plasma and urine. It uses two monoclonal antibodies, one is labelled with glucose-6-phosphate-dehydrogenase, the other one is coimmobilized together with bioluminescent enzymes from marine bacteria on the same adsorbent (Sepharose). This assay can be performed directly on 20 microliters plasma or 10 microliters urine. The protocol is very fast, no separation step is required to remove the excess labeled antibodies. The inhibitory effect of the biological sample on luminescent reaction is determined by adding NADH to the assay tubes. The working range of this assay is 3 to 300 Ul/l, with a sensitivity of detection of 0.5 Ul/l. Recovery, linearity, within and between assay precision were evaluated and appeared to be satisfactory. The authors have observed a good correlation between results obtained with our method and with radioimmunoassay.