 This is a Phase III, randomized, double-blind, double-dummy, active-comparator, parallel-arm, multicenter study to evaluate the efficacy and safety of rituximab compared with MMF in participants with moderate-to-severely active PV requiring 60-120 milligrams per day mgday oral prednisone or equivalent. Participants must have a confirmed diagnosis of PV within the previous 24 months by skin or mucosal biopsy and immunohistochemistry and evidence of active disease at screening. 