Organo-antimonyl derivatives are effective schistosomicides. Their mechanism may be d ae to the interaction between antimony and mercapto-containing enzymes in the parasites. Since it seems that Mannich bases, which are active alkylating agents, are also capable to fix the mercapto compounds, it would be interesting to see if certain Mannich bases were active against schistosomiasis. A number of Mannich bases have therefore been prepared from substituted phenols in the present woik.