INTRODUCTION AND OBJECTIVES: Methotrexate (MTX) is an antimetabolite, analogue and folate antagonist used in the treatment of malignant and non-malignant diseases that plays an important role in CNS prophylaxis, and has a different intensification strategy: Doses from 500 mg/m2 administered intravenously are defined as high-dose methotrexate (HDMTX) and are used to treat a variety of childhood neoplasms (ALL, osteosarcoma, lymphomas). MTX is considered an essential drug by the World Health Organization (WHO) because it is active against many types of cancer, and is one of the biggest successes in the pharmaceutical industry. However, the potential adverse events associated with MTX attract attention, as they represent the main cause of drug withdrawal. HDMTX therapy can cause significant toxicity, which leads to morbidity and mortality. Folate supplementation with folinic acid often mitigates the effects, reduces the incidence of hepatoxicity, hematological effects and gastrointestinal intolerance without impairing the effectiveness of MTX. The objective of this study is to present a profile of the use of patients using high dose methotrexate with their respective serum levels, together with the administration of folinic acid after infusion as a rescue therapy for children in a hematological ward of a public pediatric hospital in state of Rio de Janeiro. MATERIAL AND METHODS: This is an observational, cross-sectional and retrospective study, carried out in Chemotherapy Pharmacy of the Martagão Gesteira Childcare and Pediatrics Institute. The doses and serum levels of methotrexate and folinic acid were collected from the pharmacotherapeutic plans of patients admitted to the hematological ward from January to August/2020. The results were quantified and classified by pharmaceutical companies in the sector. The patients were separated by sex, age group and dose.RESULTS AND CONCLUSION: Seventeen children used the therapy during this period. Of the total, 65 % were boys and 35%, girls.The main diagnosis involved were LLA (76%) and the most common MTX dosages were between 4-5 g (24%) and 6-7 g (15%). In rescue therapy, Leucovorin was used at 8-28 mg average dosages. Extra doses were recorded outside the protocol. However, all match with data recommended in the therapeutic plans. This study reiterates the importance of the clinical pharmacist, in the collection, interpretation and interventions related to pharmacological therapy.