Pulmonary toxoplasmosis occurs mainly in immunosuppressed patients and its diagnosis mainly relies upon biological confirmation of the parasite. We present the case of a 47 years patient in medullar aplasia after induction chemotherapy for acute lymphoblastic leukemia that developed pulmonary infiltrates of parasitic origin. The diagnosis of pulmonary toxoplasmosis was established after identification of the parasite in brochioloalveolar lavage fluid (BAL) and peripheral blood. Serological tests are of limited utility in immunosuppressed patients. We used classical methods for the diagnosis of parasitosis but they are being replaced by molecular methods. Polymerase Chain Reaction (PCR) allows a highly specific and sensitive diagnosis on any sample but it cannot be performed in any center.