Extensive multimer formation of small and uncharged analytes was observed in electrospray mass spectrometry. The concentration-dependent aggregation behavior, including species up to tetramers, resulted in highly nonlinear calibration curves. For some analytes, these effects were operating down into the nanomolar level. Varying the drift potential failed to selectively dissociate the multimer complexes in favor of the monomer, which severely obstructed quantitative work. However, by incorporating certain cationic additives into the electrosprayed solution, complete suppression of the multimers could be obtained. In addition, a gain in the signal intensities by a factor up to 7 was achieved. A variety of additives were investigated, and the structural requirements for optimum performance will be outlined.