Four truck drivers involved in a humanitarian mission across the Sahara towards Mali fell ill 15 days after their return. Plasmodium falciparum malaria (thankfully, non pernicious) was diagnosed with 3 to 4 days delay. The four drivers had been treated with chloroquine and proguanil but the dosage may have been insufficient with regard to their body weight (average weight = 110 kg). These 4 travelers had all slept outside (in Tintane, near Kiffa in Mauritania), without any anti-vectorial protection, whereas their other 8 companions (none of whom caught malaria) had slept in their vehicles. The evolution of the 4 cases was favourable despite the difficulties involved in urgently obtaining sufficient amounts of quinine for treatment. How can these cases be explained in relation to prophylactic treatment of associated chloroquine and proguanil? One explanation might be resistance of the P. falciparum strain. We were unable to study this possibility. The high incidence and similitude of cases points towards a hypothesis of resistance both to proguanil and chloroquine. Resistance to chloroquine, as has been formally ascertained in Mauritania, reinforces such a conviction. And yet prophylaxis does not prevent pernicious malaria. This clinical form of the disease, with P. falciparum primo-invasion occurring under rigorous chemoprophylaxis is characteristic of a partially resistant strain. The most reasonable explanation besides "chance" is that we are dealing here with a partially resistant strain of Plasmodium falciparum which is thus also partially sensitive to--in this case highly effective--therapeutic treatment. Indeed, chloroquino-resistant strains are more sensitive to mefloquine and halofantrine. Another explanation might be under-dosage of Savarine with relation to the body weight of these 4 patients. We should be aware of adapting more rigorously the posology of prescribed prophylaxis. But above all, this outbreak should remind us that we should recommend to travelers and drivers planning a trip to Sub-Saharan Africa to take with them anti-vectorial protective gear. Finally, the observation of these cases indicates once more the difficulty in France of establishing a proper diagnosis in face of malaria. Health personnel must systematically call to mind malaria in face of thrombopenia or fever following a sojourn in an endemic area even when chemoprophylaxis has been correctly followed.