A study was made of ribosomes and ribonuclease in the roots of corn seedlings aged by fluoride. Fluoride induced a reduction of ribosome content in which a decrease in polysome level was accompanied by an increase in number and concentration of monosomes and subunits combined. Fluoride increased the specific activity of ribonuclease, probably associated with ribosomal protein. This enhanced activity was likely due to enzyme activation caused by fluoride. Sucrose density gradient analyses demonstrated that ribosome fractions contained a mixture of heterogeneous RNA components.