Abstract: An immunoassay method including the steps of: preparing a measuring sample by mixing a specimen with an immunoreactive substance, capable of specifically binding to a defined analyte, allowing the sample to react for a given reaction time, measuring a signal related to interactions of the immunoreactive substance with the analyte in the sample over the reaction time, checking on the basis of signals measured at different times, whether or not prozone effect has occurred in the sample and marking of a prozone-positive sample accordingly, and calculating from at least one of the signals measured during the reaction time the concentration of analyte in the sample by using a calibration curve or a portion of a calibration curve covering concentrations of analyte causing prozone effect for prozone positive samples, and another calibration curve or portion or calibration curve covering concentrations of analyte not causing prozone effect for the remaining samples.