Background. The homeostatic chemokine, CXCL13 (BLC, BCA-1), helps direct the recirculation of mature, resting B cells, which express its receptor, CXCR5. CXCL13/CXCR5 are expressed, and may play a role, in some non-AIDS-associated B cell tumors. Objective. To determine if CXCL13/CXCR5 are associated with AIDS-related non-Hodgkin's lymphoma (AIDS-NHL). Methods. Serum CXCL13 levels were measured by ELISA in 46 subjects who developed AIDS-NHL in the Multicenter AIDS Cohort Study and in controls. The expression or function of CXCL13 and CXCR5 was examined on primary AIDS-NHL specimens or AIDS-NHL cell lines. Results. Serum CXCL13 levels were significantly elevated in the AIDS-NHL group compared to controls. All primary AIDS-NHL specimens showed CXCR5 expression and most also showed CXCL13 expression. AIDS-NHL cell lines expressed CXCR5 and showed chemotaxis towards CXCL13. Conclusions. CXCL13/CXCR5 are expressed in AIDS-NHL and could potentially be involved in its biology. CXCL13 may have potential as a biomarker for AIDS-NHL.