Alkalinization of culture medium is accompanied by a considerable increase in the putrescine production by Escherichia coli and its efflux in the environment. Existence of the reversible putrescine (+2)/2K(+) exchange was shown under conditions of inhibition and energy limitation of the main potassium transport systems. It is assumed that this exchange serves as an alternative mechanism of potassium transport for providing continuous functioning of K+/H+ antiporter.