The factors directing marginal zone B cells to the splenic marginal zone are not well understood. Here we report that FTY720, a drug that targets sphingosine 1-phosphate (S1P) receptors, induced marginal zone B cell migration into follicles. Marginal zone B cells expressed S1P receptors 1 and 3 (S1P₁ and S1P₃, respectively). Using gene-targeted mice, we show that S1P₁ but not S1P₃ was required for localization in the marginal zone. In mice lacking the chemokine CXCL13, S1P₁-deficient marginal zone B cells reacquired a marginal zone distribution. Exposure to lipopolysaccharide or antigen caused marginal zone B cells to downregulate S1P₁ and S1P₃ and to migrate into the splenic white pulp. These data suggest that marginal zone B cell localization to the marginal zone depends on responsiveness to the blood lysophospholipid S1P, with S1P₁ signaling overcoming the recruiting activity of CXCL13.