The effect of introducing an immobilized metal ion ligand in the lower phase of the PEG/Dextran system was studied on the erythrocytes and lymphocytes partition. The ligand in the lower phase was added as an insoluble form [Sepharose-IDA-M(II)] with or without a ligand in the upper phase. We first checked that the addition of the insoluble ligand in the system did not affect the phase volume and settling, and also that Sepharose-IDA-M(II) partitioned strictly in the lower phase. Then we studied the partition of cells with various concentrations of ligand in the lower and upper phases. We clearly demonstrate here that the partition in immobilized metal ion affinity partitioning (IMAP) systems is correlated with the affinity between the cell surface and the ligand. Cells are attracted to the ligand-containing phase. This fact is important not only for the greater understanding of IMAP, but could also for the separation of some types of cells.