The study of the multipls formas of serum alkaline phosphatase in patients with schistosomiasis (hepato intestinal compensated and decompesated hepatosplenic) revealed modifications in their physico-chemical properties. Molecular filtration with a Sephadex G-200 colun separated three distrinct molecular forms of serum alkaline phosphatase in patients with hepatosplenic schistosomiasis mansoni. Two of these forms presented as thermoresistant, contrasting with the equivalente multpls forms in normal serum which are termolabile, In the hepatointestinal phase of schistosomiasis mansoni only one thermolabile form of alkaline phosphatase was isolated which corraparded to twe primary isodynamic form in normal serum. Studies were also done on the different molecular forms of human alkaline phosphatase. From live, small intestine, bone and placenta, originating from tissues considered as normal, and from Schistosoma mansoni itself.