crystallographic screening towards EfTS. We obtained two X-ray crystallographic structures: the first with a weak phthalimidic inhibitor bound in one subunit and 5-hydroxymethylene-6-hydrofolic acid (5-HMHF) in the other subunit; a second X-raystructure complex with methotrexate. The structural information achieved confirm the role of EfTS as an enzyme involved in the folate pool system and provide a structural