Dynamics of the response of tobacco cells (line BY-2) to exogenous cytokinin, N-6-benzyladenine, and cyclin-dependent kinase inhibitor, roscovitine, was followed using alginate-immobilized cells packed into a column. N-6-Benzyladenine (1.25 muM) increased the synthesis of the physiologically-active endogenous cytokinin, isopentenyladenosine, in the effluent up to 0.1 nM. Simultaneously, conversion of the excess of endogenous cytokinins to biologically inactive derivatives of cis-zeatin occurred, up to 0.8 nM. Roscovitine (50 muM) further increased cis-cytokinins, up to 2.2 nM.