Background. The modern concept of acute leukemia therapy involves stratification of patients into prognostic risk groups and a differentiated approach to treatment based on prognostic factors. However, antitumor treatment, including cytostatics, targeted agents, immunotherapy, cellular technologies, is not always highly effective, especially in patients with a poor prognosis. The development of new high-tech diagnostic methods and the refinement of leukemia prediction models remain an urgent clinical task.Aim. To demonstrate the fundamental capabilities of the nuclear gamma resonance method in the early diagnosis of leukemia.Materials and methods. The blood of 1 healthy man and 5 patients of different genders and ages with leukemia was examined. Gamma-resonance (Mossbauer) spectra of iron nuclei in their blood were analyzed.Results. Significant differences in the parameters of the spectra of 57Fe nuclei in the blood of both healthy men and patients of different genders and ages were revealed.Conclusion. Nuclear gamma-resonance spectroscopy at the atomic-nuclear level reveals the influence of cancer cells on the state of iron nuclei and, consequently, on the state of blood. This method can be used both for early diagnosis of leukemia and for assessing the population of tumor cells after achieving cytological remission in leukemia.