The effect of a range of inhibitors on kinetin-induced increase in fresh weight (expansion) and in RNA content of isolated cotyledons of fenugreek (Trigonella foenum-graecum L.) has been measured over incubation periods of up to 48 h in darkness. Some compounds inhibited both expansion and net RNA increase: 2, 4-dinitrophenol, cycloheximide, L-azetidine-2-carboxylic acid, 6-methylpurine, thiouracil, and actinomycin D. Other compounds inhibited net RNA increase but not expansion: 5-fluorouracil, 2, 6-diamino-purine, 5-azacytidine, and L-ethionine. Ethionine stimulated the induction of nitrate reductase. Effects by ethionine on RNA content were reversed by methionine, but not by adenosine. Inhibitory interactions between ethionine and guanosine, hypoxanthine and especially some 6-substituted adenines were observed. Ethionine, apart from inhibiting uptake of labelled uridine, also inhibited its incorporation into rRNA but not that into tRNA. Results confirm that kinetin-induced expansion in cotyledons is dependent on mRNA synthesis and suggest that the inhibitory effect of ethionine on kinetin-induced RNA increase is not due to ATP trapping or inhibition of protein synthesis or reduced methylation of tRNA, but to interference with the metabolism of rRNA.