Polyamines (PAs), important regulators of plant growth and development, when applied to tobacco and chrysanthemum in vitro cultures, had varied morphogenic responses, depending on the morphogenic programme (callogenic, caulogenic, rhizogenic or somatic embryogenic). Putrescine and spermidine at 2 mg l^-1, significantly stimulated tobacco callogenesis and rhizogenesis, the latter also stimulated by spermine, while putrescine and spermine, and spermine and spermidine stimulated chrysanthemum 'Lineker' and 'Shuhou-no-chikara' rhizogenesis, respectively. None of the PAs stimulated any other morphogenic programme in chrysanthemum, and the exogenous application of cadaverine inhibited adventitious root and shoot formation in both tobacco and chrysanthemum. Despite their positive effect on morphogenesis when applied exogenously, PAs may have a negative impact if the endogenous levels are already high, this probably depending on the developmental state of the tissue in a particular developmental programme. Endoreduplication was prominent in tobacco callus cultures, with or without the addition of PAs. Despite some negative effects by cadaverine on chrysanthemum in vitro cultures, plants derived from any PA treatment resulted in normal greenhouse growth and flowering.