AbstractHuman bone‐derived cells, grown in monolayer culture, were dissociated by incubations with trypsin/EDTA and subjected to thin‐layer counter‐current distribution in a ‘low potential’ aqueous two‐phase system. Two major populations of cells were detected. The number of cells in the second (more hydrophobic) population increased with length of trypsinization and time in culture. Cells allowed to ‘regain’ surface molecules lost by trypsinization did not produce the second population.Cells occupying the second population after a short period of trypsinization had a lower rate of division than peak 1 cells but showed a higher rate of protein synthesis per rate of division than peak 1 cells.These results show that the cells have markedly different sensitivities to trypsin digestion which may be related to cell division rate of growth. The possible relationship between this and osteoblast developmen