Matrix metalloproteinases (MMPs) are expressed by T cells and macrophages, but there is a paucity of evidence for their role in immune responses. We have studied mice with deficiencies of stromelysin-1 (MMP-3) or gelatinase B (MMP-9) in a dinitrofluorobenzene (DNFB)-induced model of contact hypersensitivity (CHS). Stromelysin-1-deficient mice showed a markedly impaired CHS response to topical DNFB, although they responded normally to cutaneously applied phenol, an acute irritant. Lymphocytes from lymph nodes of DNFB-sensitized stromelysin-1-deficient mice did not proliferate in response to specific soluble antigen dinitrobenzenesulfonic acid, but did proliferate identically to lymph node lymphocytes from wild-type mice when presented with the mitogen Con A. An intradermal injection of stromelysin-1 immediately before DNFB sensitization rescued the impaired CHS response to DNFB in stromelysin-1-deficient mice. Unlike stromelysin-1-deficient mice, gelatinase B-deficient mice exhibited a CHS response comparable to wild-type controls at 1 day postchallenge, but the response persisted beyond 7 days in contrast to the complete resolution observed in wild-type mice by 7 days. However, gelatinase B-deficient mice had a normal rate of resolution of acute inflammation elicited by cutaneous phenol. Gelatinase B-deficient mice failed to show IL-10 production at the site of CHS, an essential feature of resolution in control mice. These results indicate that stromelysin-1 and gelatinase B serve important functions in CHS. Stromelysin-1 is required for initiation of the response, whereas gelatinase B plays a critical role in its resolution.