Rituximab is an anti-CD20 monoclonal antibody that has efficacy in B-cell non-Hodgkin s lymphoma (NHL). Adjuvant immunotherapy with rituximab may reduce relapse rates for high-risk B-cell NHL following high-dose chemotherapy with autologous stem cell transplantation (SCT). However, the potential adverse effects of rituximab on immune reconstitution following SCT are not fully characterized. We performed a retrospective analysis of immunoglobulin (Ig) levels and peripheral blood neutrophil counts in 11 patients who received adjuvant rituximab following autologous SCT for B-cell NHL. Results were compared to a contemporaneous group of 24 patients who received an identical conditioning regimen and autologous SCT for lymphoma, but no adjuvant rituximab. Adjuvant rituximab was associated with a significantly increased incidence of hypogammaglobulinaemia between 12 and 24 months post-SCT, but not neutropenia. Despite suppression of Igs, there were no late or atypical infective complications attributable to rituximab.