In order to grow, solid tumors need to develop new blood vessels. Neoplastic cells secrete growth factors that stimulate angiogenesis and tumor growth. Since Carrageenan acts as in vitro blocking agent which interferes with growth factor-receptor binding, we tested its action in vivo in order to analyze its growth inhibition capability in an experimental murine fibrosarcoma model. Indomethacin was used as a non-steroidal anti-inflammatory agent to neutralize the inflammatory action of Carrageenan. A murine fibrosarcoma was induced with methylcholanthrene in Balb/c mice and maintained by serial passage of tumor cells in mice of the same strain. Tumor volume was evaluated measuring two dimensions and applying the formula V = 0.4 x d2 x D. The mice with tumors were separated into groups; one of them was used as control and the other ones were treated with Indomethacin, Carrageenan and Carrageenan-Indomethacin. Tumor volume was compared between groups using the Student t Test. We demonstrated that Carrageenan and Indomethacin inhibit tumor growth. The inhibitory action of Carrageenan is significantly higher than the antitumoral effect of either Indomethacin or Carrageenan-Indomethacin.