Six compounds, all newly synthesized triazole-pyrimidine derivatives that proved inhibitory of in in vitro growth of epimastigotes in Trypanosoma cruzi and of promastigotes of Leishmania donovani and Phytomonas staheli, were studied to investigate their toxic effects. As a biological model, the plant trypanosome P. staheli, which causes sudden wilt in the oil palm and Hartrot in the coconut palm, was used. The six compounds markedly inhibited macromolecule synthesis (nucleic acids and proteins) by the parasite. The cells treated with these compounds present severe damage in their ultrastructure-intense 'vacuolization, and appearance of lysosomes as well as other residual bodies. The mitochondrial section appeared larger in size. with a swollen matrix. In addition, these compounds changed the excretion of end metabolites, primarily affecting ethanol and acetate excretion, possibly by directly influencing certain enzymes (alcohol dehydrogenase and acetate synthetase) or their synthesis. 2000 Elsevier Science Ltd.