LPA and SIP act synergistically with SDF-1 in primitive hematopoietic cells. The effect of LPA or S1P on the migratory response of cells to SDF-1 was measured. In some wells no additional stimuli were used (NA). In some wells LPA, S1P, and SDF-1 were added to either the top well (shown as LPA/NA on the x-axis), the bottom well (NA/LPA), or both. Data are expressed as the fold increase in cell migration, where the migration stimulated by SDF-1 alone is 1. Results are the mean ± SEM of 3 or more experiments. Statistical analysis was by Student paired, 2-tailed t test.