This is a Phase III, open-label, multicenter, randomized, comparative study of Campath versus chlorambucil as front line therapy in patients with progressive B-Cell Lymphocytic Leukemia (B-CLL). Eligible patients must have previously untreated, Rai stage I-IV disease, and be experiencing progression of their B-CLL requiring treatment. Patients who meet all eligibility criteria may be randomized on a 1:1 basis to receive either Campath or chlorambucil. An estimated 284 patients (142 per treatment arm) from approximately 40 or more investigational sites will be randomized to one of the two treatment arms.