The cellular slime mold Dictyostelium discoideum expresses a RecA homolog that is distributed in mitochondria. A gene disruption mutant is hypersensitive to DNA-damaging agents, indicating that RecA is required for the repair of mitochondrial DNA. We analyzed the process by which a multicellular structure of recA^- cells is formed. Four hours after starvation, the internal glucose level of recA^- cells (11.8±0.9 nmol/mg protein) was higher than that of wild-type cells (6.7±0.1 nmol/mg protein). The degree of cell-cell adhesion of recA ^- cells was greater than that of wild-type cells, while the migration speed of recA^- cells (3.5±0.2 μm/min) was less than that of wild-type cells (4.3±0.3 μm/min). The increase in cell-cell adhesion and decrease in motility of recA^- cells gave rise to the formation of large multicellular structures. The diameters of mounds formed by recA^- and wild-type cells were 0.30±0.01 mm and 0.17±0.01 mm, respectively.