Proteolytic processing is an important regulatory mechanism for chemokines. Matrix metalloproteinases (MMPs), such as gelatinase A/MMP-2 and gelatinase B/MMP-9, are known to process the aminoterminal end of various chemokines, including interleukin-8 (IL-8/CXCL-8) and monocyte chemotactic protein-3 (MCP-3/CXCL-7). In the present study, two proteases, gelatinase B and neutrophil collagenase/MMP-8, are shown for the first time to process the carboxyterminal end of two chemokines, monokine induced by interferon (IFN)-gamma (MIG/CXCL-9) and IFN-inducible protein-10 (IP-10/CXCL-10). Neutrophil collagenase degrades MIG into small fragments and cleaves IP-10 behind positions 71 and 73. Gelatinase B degrades IP-10 and cleaves MIG at three different sites in its extended carboxyterminal region. This results in the formation of MIG(1-94), MIG(1-93), and MIG(1-90). In general, gelatinase B was more efficient than neutrophil collagenase in processing these chemokines. Alignment of the CXC chemokines with the respective cleavage sites by both MMPs identified the ELR motif as a possible determinant for amino terminal cleavage by these MMPs.