We describe time-resolved fluoroimmunoassay for human choriogonadotropin involving monoclonal antibodies directed against the beta- and alpha-subunits. The latter antibody was labeled with europium, which was measured by counting for 1 s after the immunoreaction was completed. In the solid-phase sandwich assay, both a one-step and two-step procedure were used; the respective measuring ranges were 0.7-135 and 0.7-350 int. units/L, the latter covering a 500-fold dynamic range. The CV within the assay range was between 4 and 8%, depending on the dose. Cross reactivity with lutropin in the one- and two-step procedures was 1.6% and 1.0%, respectively.