Abstract: A method of determining free analyte level in a sample containing the analyte in free and bound portions is accomplished in sequential steps as follows. The sample is combined with a known first liquid volume containing soluble anti-analyte receptor in excess of the free analyte in the sample. The resultant mixture is incubated for a period of time sufficient to allow the binding reaction of the free analyte with the anti-analyte receptor to reach substantial completion to form a first incubation mixture. A known second liquid volume is added thereafter which contains soluble conjugate sufficient to reduce the sample proportion in the resultant mixture to no greater than 10% v/v, with the conjugate comprising a labeled analyte or labeled analog thereof, to allow the conjugate to bind with the anti-analyte receptor not bound in the first incubation mixture to form a second incubation mixture.