Mast cells infiltrate kidneys of humans with crescentic glomerulonephritis (GN), and the degree of infiltrate correlates with outcome. However, a functional role for mast cells in the pathogenesis of GN remains speculative. GN was induced by intravenous administration of sheep anti-mouse glomerular basement membrane globulin. After 21 d, systemic immune responses and disease severity were analyzed in wild-type, mast cell–deficient (W/Wv), and bone marrow–derived mast cell–reconstituted W/Wv mice (BMMC→W/Wv). There were no significant differences in the humoral response toward the nephritogenic antigen or in memory T cell number among the three groups; however, antigen-stimulated T cell IFN-γ production was significantly elevated in BMMC→W/Wv mice. Dermal delayed-type hypersensitivity in W/Wv mice was reduced compared with wild-type and BMMC→W/Wv mice. No mast cells were detected in kidneys of W/Wv mice with GN, whereas in BMMC→W/Wv mice, the numbers of renal mast cells were similar to wild-type mice with GN. W/Wv mice were protected from the development of crescentic GN, exhibiting reduced crescent formation (10 ± 1% c.f. 36 ± 2% in wild type), glomerular influx of T cells/macrophages, and interstitial infiltrate compared with wild-type mice. In contrast, BMMC→W/Wv demonstrated a similar severity of GN as wild-type mice (35 ± 2% crescentic glomeruli), accompanied by a prominent inflammatory cell infiltrate into glomeruli and interstitial areas. Glomerular expression of intercellular adhesion molecule-1 and P-selectin were reduced in W/Wv mice but restored to wild-type levels in BMMC→W/Wv mice. These findings suggest that renal mast cells mediate crescentic GN by facilitating effector cell recruitment into glomeruli via augmentation of adhesion molecule expression.