PURPOSE OF REVIEW: Malignancy is characterized by a systemic deficiency of glutamine (GLN). The debate over whether GLN supplementation should be standard of cancer patients is still topical. This review focuses on recent findings on the effect of GLN administration on the incidence and severity of adverse effects in host due to radiotherapy or chemotherapy or both and on its putative adjuvant role on cytotoxicity of radiotherapy and chemotherapy on tumour. RECENT FINDINGS: Animal and human studies have reported that high-dose GLN supplementation could prevent gastrointestinal tract injury after radiotherapy and chemotherapy. Animal studies are suggesting that GLN could actually decrease tumour growth by upregulating the immune system and through a regulation of the redox status associated to the metabolism of glutathione. GLN could enhance the selectivity of antitumour drugs by protecting normal tissues from chemotherapy and by sensitizing tumour cells to chemotherapy. SUMMARY: Recent studies have shown that GLN could have dichotomic actions in host versus in tumour, probably in link with glutathione metabolism, suggesting that GLN could be used in clinical practice to increase the therapeutic index of oncological treatments.