2. Hold continuous dosing with rituximab with re-dosing upon a significant ANCA titer increase: For MPO, a significant increase will be defined as a 5-fold rise in ANCA titer and a level greater than 4 times the cutoff value for the assay. For PR3, a significant rise will be defined as a 4-fold rise in ANCA titer to a level at least twofold above the cutoff for the assay. Subjects will not receive regularly scheduled every six-month doses of rituximab and will instead be monitored every three months. Subjects who sustain a significant increase in ANCA titer will receive rituximab 1000mg IV x 2 doses, ~2-3 weeks apart. If the ANCA titer remains two-fold above baseline and above a specified threshold (the cutoff value of the assay for PR3 and 4 times the cutoff value for MPO) , subjects will continue to receive rituximab 1000mg IV every 6 months for a maximum of 2 doses, at which time a new baseline ANCA titer will be established and the cycle will re-start.