The effects of polyamines (agmatine, cadaverine, putrescine, spermidine and spermine) on the activity of the main aminopeptidases (AP I and AP II) from Lactobacillus sake were determined. Concentrations in the range of 1 mM caused 6–25% inhibition of AP I except for spermine (45% inhibition). Higher polyamine levels (5–10 mM), except for putrescine, exerted a stronger inhibition (20–60%) on AP I. Agmatine and putrescine also reduced AP II activity (6–25%) at concentrations of 0.1–10 mM while cadaverine did not have a notable effect. Spermidine and spermine stimulated (15–70%) the activity of AP II at concentrations >1 mM. Thus, control of polyamine levels is important because they are a potential hazard for human health and also because of their effects on aminopeptidase activity.