Excised cotyledons of radiata pine (Pinus radiataD. Don) were cultured in the presence or absence of benzyladenine and two concentrations of dicyclohexylamine, a potent inhibitor of spermidine synthesis in animals and bacteria. Cellular levels of the drug and of putrescine, spermidine and spermine were determined by dansylation followed by thin layer chromatography. The rate of uptake of the drug was rapid during the first 6 h of incubation and then diminished; nevertheless, its cellular content increased with time in culture and uptake was greater if more was present in the medium. Cotyledons cultured on benzyladenine‐containing media accumulated more dicyclohexylamine than on benzyladenine‐free media and this resulted in toxic side‐effects. The drug had no significant effect on the elongation growth occurring in the absence of the hormone. In cotyledons treated with the drug, spermidine levels fell to zero after a 5‐ to 10‐day exposure. Putrescine increased transiently at 24 h and then declined significantly. Spermine levels also declined to 11% of control values by day 5 and remained low throughout. Except for a marked decrease in all three polyamines during the first 24 h of culture, all control cotyledons maintained significantly higher polyamine levels than dicyclohexylamine‐t