A comparison has been made between different immunomagnetic techniques for separating normal human mammary epithelial cells based on the exclusive expression of EMA (epithelial membrane antigen) by luminal cells and CALLA (CD10) by myoepithelial cells. When cells labelled with antibodies to these antigens were incubated with Dynabeads, they rosetted myoepithelial but not luminal cells. However, both luminal and myoepithelial cells could be positively separated using the MACS system. Purity was established by analyzing the expression of CALLA and EMA using flow cytometry, and of cell-type specific cytokeratins using indirect immunofluorescence. Dynabead-separated myoepithelial cell populations were of high purity (> 98%) but the beads could not be removed from the cells. Luminal cell populations separated by the MACS method were also highly purified (> 95%), as were myoepithelial cell populations (> 90%). Using this immunomagnetic separation method, up to 10(7) cells of each type could be obtained from individual preparations.