Changes in ribosome populations in artichoke tuber slices aged in water and treated with 2,4-D and kinetin were followed using fractionation and density gradient techniques. A decline in total ribosomes occured during aging due to a drop in the free ribosome population. At the same time membrane bound(m.b.) ribosomes increased significantly. Isotope labelling indicated that extensive ribosome synthesis occured during this period with new ribosomes being randomly distributed between free and m.b. populations. Aging in 5FU prevented formation of m.b. ribosomes without affecting levels of free ribosomes. 5FU markedly changed the sedimentation characteristics of cytoplasmic RNA. Free polysomes gradually increased to a maximum by 24 hr of aging. Membrane bound ribosomes were also predominantly in polysomes. Aging in 5FU did not prevent formation of free polysomes. Hormone treatment significantly increased the total and free ribosome population and slightly elevated the proportion of free ribosomes in polysomes.