The synthesis and in-vitro antiprotozoal evaluation of novel N(4)-(benzyl)spermidyl-linked bis(1,3,5-thiadiazinane-2-thione) (bis-THTT) derivatives from N(4)-(benzyl)spermidine is disclosed. Several of the new bis-THTT have in-vitro activities against L. donovani and T. cruzi that are comparable or superior to those of currently employed protozoocidal agents.