Factors influencing the sensitivity, or the signal/noise ratio.of dissociation enhanced lanthaqide fluoroimmunoassay (DELFIA) have been studied. The fluorescence responses and signal/noise ratios for different europium amount were shown to be changed with the volume of enhancement solution.and there was an optimum volume at a certain europium amount.The smallest europium amount leads to the smallest optimum volume.20/00 of the net fluorescence intensity was increased by using tinfoil reflection layer. Effective washing and drying methods of microtitration strips decreased background fluorescence have been developed.