Inflammatory cells are postulated to mediate some of the brain damage following ischemic stroke. Intracerebral hemorrhage is associated with more inflammation than ischemic stroke. We tested the sulfated polysaccharide fucoidan, which has been reported to reduce inflammatory brain damage, in a rat model of intracerebral hemorrhage induced by injection of bacterial collagenase into the caudate nucleus. Rats were treated with seven day intravenous infusion of fucoidan (30 micrograms h-1) or vehicle. The hematoma was assessed in vivo by magnetic resonance imaging. Motor behavior, passive avoidance, and skilled forelimb function were tested repeatedly for six weeks. Fucoidan-treated rats exhibited evidence of impaired blood clotting and hemodilution, had larger hematomas, and tended to have less inflammation in the vicinity of the hematoma after three days. They showed significantly more rapid improvement of motor function in the first week following hemorrhage and better memory retention in the passive avoidance test. Acute white matter edema and eventual neuronal loss in the striatum adjacent to the hematoma did not differ between the two groups. Investigation of more specific anti-inflammatory agents and hemodiluting agents are warranted in intracerebral hemorrhage.