In an attempt to ameliorate chemotherapy-induced side-effects after transplantation of autologous peripheral blood stem cells (PBSCT), we tested the reinfusion of autologous macrophages (MAC) that are known to be potent antimicrobial effector cells and cytokine producers. Ten patients were treated with two sequential cycles of high-dose chemotherapy followed by PBSCT. Before the second cycle of PBSCT, mononuclear cells were harvested, cultured for 8 d in order to induce MAC maturation and reinfused 3 d after PBSCT without clinical problems. However, MAC infusions did not substantially alleviate the toxicity of autologous PBSCT.