Diagnosis and monitoring of reactivated toxoplasmosis (RT) in HSCT recipients was introduced into the transplantation practice in Serbia in 2013 (cooperation of the Mother and Child Health Care Institute and the NRL for toxoplasmosis). Despite its many benefits, clinical experience with this approach to control T. gondii infection in HSCT patients has also revealed gaps including diagnostic challenges pertinent for decisions on treatment, and lack of consensus on the frequency and duration of blood sample monitoring by qPCR after HSCT, respective of clinical setting and administration of prophylaxis. Thus, the goal of the proposed project is to, after standardization and harmonization of the qPCR protocol in both partner laboratories, identify subgroups of patients (according to the clinical setting, type of prophylaxis etc.) at the highest risk of RT, that would benefit the most from systematic PCR monitoring, with the final outcome to devise a cost-effective alternative for the prevention of RT after HSCT.