The dissociation of free ribosomes at elevated concentrations of KCl is dependent on hydrostatic pressure. The pressure necessary for the dissociation is determined for KCl concentrations ranging from 0.1-0.4 M. It varies between 425 kg cm(-2) at 0.1 M and 10 kg cm(-2) at 0.4 M. The partial dissociation of complex ribosomes in KCl is dependent on hydrostatic pressure in the same way as the complete dissociation of free ribosomes. Therefore, it is concluded that mRNA and peptidyl-tRNA do not contribute to the stability of the ribosome under these conditions.