Participants with NHL and MM who have undergone prior cyto-reductive chemotherapy, are to be autologously transplanted, and meet the inclusion/exclusion criteria are eligible to enter the study. The only change to the standard of care is the addition of plerixafor to a granulocyte colony-stimulating factor (G-CSF) mobilization regimen on the day prior to apheresis. Participants will undergo mobilization with G-CSF (10 mcg/kg each day) and will receive plerixafor (240 mcg/kg) in the evening prior to apheresis. Participants will undergo apheresis for up to 5 consecutive days in order to collect the target number of CD34+ stem cells (≥ 5*10^6 CD34+ cells/kg for either single or tandem transplant). After apheresis, all participants will be treated with high-dose chemotherapy in preparation for transplantation. Participants will be transplanted with cells obtained from the G-CSF and plerixafor mobilization regimen. The increase in CD34+ cells in the peripheral blood from the time of the plerixafor dose to just prior to apheresis and the number of CD34+ cells in the apheresis product will be measured. Success of the transplantation(s) will be evaluated by the time to engraftment of polymorphonuclear leukocytes (PMN). A subpopulation will have pharmacokinetic and pharmacodynamic analysis done.