In a severe case of malaria, the chemosensitivity of a Plasmodium falciparum strain from a traveller to Tanzania who underwent chemoprophylaxis treatment with chloroquine (600 mg weekly) was evaluated in vitro. In the 28 hours maturation assay and a 72 hours proliferation assay, the strain proved to be highly resistant to chloroquine and to have a reduced sensibility to the sulfadoxin - pyrimethamin association.