Radioimmunotherapy with 90Y Ibritumomabu (Zevalin, BSP) is a new method of systemic radiotherapy applicable to B-cell lymphoma patients. It may be delivered as a short outpatient procedure, with few adverse effects other than hematological toxicity. In the paper, we present length and depth of cytopenias, together with the results of additional tests performed to reveal the possible pathomechanisms, based on 102 patients treated at the University Hospital in Krakow.