Sulphated polysaccharides from marine algae are widely used in biotechnological and pharmaceutical areas. In this study, we evaluated the effects of sulphated polysaccharides from the green marine alga Caulerpa mexicana (Cm-SPs) in nociceptive and inflammatory models in rodents. Cm-SPs (10 or 20 mg/kg), administered i.v. in Swiss mice, significantly reduced nociceptive responses, as measured by the number of writhes in response to acetic acid. Cm-SPs (10 or 20 mg/kg) also reduced second-phase responses in the formalin test, but did not exhibit a significant antinociceptive effect in the hot plate test, suggesting that its antinociceptive action occurs through a peripheral mechanism. Cm-SPs (5, 10 or 20 mg/kg), administered s.c. in wistar rats 1 hr before carrageenan, dextran, histamine or serotonin, were tested in paw oedema models. Cm-SPs (10 or 20 mg/kg) reduced carrageenan-induced paw oedema and myeloperoxidase activity in the paw. In addition, Cm-SPs (20 mg/kg) inhibited dextran- or histamine-induced paw oedema, but not serotonin-induced oedema, suggesting that histamine is the major target of Cm-SPs anti-oedematogenic activity. Finally, Cm-SPs (20 mg/kg) administered in mice did not show significant signs of toxicity. In conclusion, Cm-SPs appear to be promising natural modulatory agents for pain and inflammatory conditions.