Several peptide sequences in laminin α1, the α-chain of laminin (Ln)-1, mediate biological responses in vitro, but Ln-1 is rare in vivo. Since Ln-5 and Ln-10, which contain the α3 and α5 chains, respectively, are the most prominent laminin heterotrimers in normal adult tissues and few functional domains in other laminin chains have been identified, we are investigating the α3 and α5 chains for biological activities. Incubation of mouse macrophages with the laminin α5 peptide AQARSAASKVKVSMKF resulted in marked increase in matrix metalloproteinase (MMP)-9 mRNA and gelatinolytic activity in the conditioned media, whereas the corresponding α3 peptide QQARDAANKVAIPMRF had no effect. AQARSAASKVKVSMKF also induced expression of MMP-14, while MMP-2, MMP-3, MMP-7, MMP-12, and MMP-13 were not induced by this peptide. Deletion analyses indicated that a minimal sequence of ASKVKVSMKF was sufficient for increasing MMP-9 expression. AQARSAASKVKVSMKF was also chemotactic for neutrophils and macrophages in vitro, and induced accumulation of neutrophils and macrophages in lung airspaces in vivo following intranasal instillation into mice. Comparable accumulation occurred in MMP-9-deficient mice, indicating that MMP-9 was not required for AQARSAASKVKVSMKF-induced inflammatory cell emigration in the lung. A scrambled version of the minimal peptide, KAKSFVMVSK, was inactive. These data indicate that laminin α5-derived peptides can induce inflammatory cell chemotaxis and metalloproteinase activity.