A small pilot with 55 patients was undertaken at Memorial Sloan Kettering Cancer Center to determine whether priming with rituximab reduced the incidence and severity of HSR. Rituximab lines were primed with active drug and data were collected for 3 months on all patients receiving rituximab. These data were compared with 3 months of retrospective data with 50 patients in whom the rituximab line was primed with a diluent. The incidence and grade of HSR were measured using National Cancer Institute Common Terminology Criteria for Adverse Events.