Bothrops atrox crude venom injected intraperitoneal (i.p.) into BALB/c mice induced local afflux of inflammatory cells, one neutrophil-rich peak after 6h and another macrophage-rich peak after 48h. A similar pattern of local cell afflux plus edema, Delta lesions of some skeletal muscle cells, and hemorrhage were observed in mice intramuscular (i.m.) injected with the venom. Measurement of serum cytokines in neutrophil-depleted (by anti-mouse rat monoclonal antibody (mAb) RB6-8C5) and non-depleted BALB/c mice was performed by ELISA. With the exception of IL-1β (78pg/ml), higher levels of IL-6 (1348pg/ml), MIP-1β (437pg/ml) and MIP-2 (904pg/ml) were observed in neutrophil-depleted mice, in comparison to the values found in non-neutrophil depleted mice: IL-1β (437pg/ml), IL-6 (750pg/ml), MIP-1β (165pg/ml) and MIP-2 (90pg/ml). TNF-α was not detected. NO was detected (18μM) 24h after venom injection in neutrophil-depleted mice. RT-PCR using representative primers detected expression of mRNA in cells from BALB/c mice injected with B. atrox venom: (a) for IL-1β, IL-6, inducible nitric oxide synthase (iNOS), CXCR2, MIP-2 and RANTES in cells from mice that were neutrophil-depleted or not; (b) for CCR1, CCR5 and MIP-1β in cells from neutrophil-depleted mice; (c) for MIP-1α in cells from non-neutrophil-depleted mice; (d) TNF-α and TGF-β were not detected in either of the mice. These results indicate that neutrophils play a role in regulating the production of some cytokines and chemokines as well as locally expressed or liberated iNOS/NO in tissues injected with B. atrox crude venom.