As a result of transfecting Dictyostelium discoideum with an actin 6/lacZ fusion transgene, strain HW80 was created which expresses the β-galactosidase gene product uniformly throughout development. When mixed with an excess of unmarked wild-type cells, however, HW80 cells selectively migrate to the positions of anterior-like cells surrounding the prespore cell mass, and differentiate as if they were anterior-like cells. As the proportion of HW80 cells is increased, they also sort to positions adjacent to anterior-like cells and some differentiate as prespore cells. Thus sorting of HW80 cells toward the opposite ends of the prespore cell zone supersedes how they differentiate, suggesting that position influences whether cells differentiate as anterior-like or prespore cells.