Highlights • Despite intrathecal administration, rituximab was detectable in the serum but not the CSF. • CSF BAFF fell following rituximab administration, but serum BAFF increased. • Serum CD20+ and CD19+ cell populations fell in the peripheral blood compartment following rituximab administration. Abstract Objectives Clinical trials of IV-rituximab have proved successful. It is unclear whether intrathecal (IT)-rituximab is more efficacious at lower doses. We examine its effects on B-cell biomarkers.