Abstract Im mobilized tobacco cells excreted only a small proportion of their main secondary metabolite caffeoylputrescine into the culture medium . Experiments designed to release more of the com pound by permeabilization caused the loss of caffeoylputrescine, probably by oxidative reactions. Moreover, rather mild treatments with permeabilizing agents (e.g. n-propanol) resulted in severe growth inhibition. The ability of permeabilized cells to form caffeoylputrescine and other hy-droxycinnam oyl conjugates from phenylalanine decreased considerably even when such cells were still able to metabolize phenylalanine into various ethyl acetate extractable com pounds (e.g. hydroxycinnamic acids and acetophenones). The formation of new biotransformation products suggests that permeabilized cells could be used as a tool for testing the enzymatic capabilities of a cell culture.