Snai1 (Snail) and Snai2 (Slug), the two main members of Snail family factors, are important mediators of epithelial-mesenchymal transitions and involved in tumor progression. We recently reported that Snai1 plays a major role in tumor growth, invasion and metastasis, but the contribution of Snai2 to tumorigenesis is not yet well understood. To approach this question we have silenced Snai2 and/or Snai1 by stable RNA interference in two independent mouse skin carcinoma (HaCa4 and CarB) cell lines. We demonstrate that Snai2 knockdown has a milder effect, but collaborates with Snai1 silencing in reduction of tumor growth potential of either carcinoma cell line when injected into nude mice. Importantly, Snai1 or Snai2 silencing dramatically influences the metastatic ability of squamous carcinoma HaCa4 cells, inducing a strong reduction in liver and lung distant metastasis. However, only Snai1 knockdown has an effective action on invasiveness and fully abolishes tumor cell dissemination into the spleen. These results demonstrate that Snai1 and Snai2 collaborate on primary tumor growth and specifically contribute to site-specific metastasis of HaCa4 cells. These data also indicate that Snai1 is the major regulator of local invasion, supporting a hierarchical participation of both factors in the metastatic process.