Semicarbazide-sensitive amine oxidase (SSAO) is a multifunctional enzyme with different biological roles that depend on the tissue where it is expressed. Because SSAO activity is altered in several pathological conditions, we were interested in studying the possible regulation of the human enzyme activity. It has been previously reported that SSAO activity is increased in the presence of Dulbecco's modified Eagle medium (DMEM) in vitro. The aim of the present work was to investigate the effects of the different constituents of DMEM on human SSAO activity. We found that sodium bicarbonate was the only component able to mimic the enhancement of both human aorta and plasma SSAO activity in vitro, suggesting a possible physiological role of bicarbonate as an intrinsic modulator of the human enzyme. Failure to take this activating effect into account could also result in inaccuracies in the reported tissue activities of this enzyme.