Introduction. HIV infection is one of the most relevant diseases from a medical, epidemiological and social point of view. Timely diagnosis, detection and control of the disease, adequate prescription of antiretroviral therapy can sufficiently reduce the viral load on the patient's body, reduce the risk of transmission of infection. Currently, combinations of various antiretroviral drugs are increasingly being prescribed as therapy. One of the most important is combination of atazanavir and ritonavir. The most important stage for the study of pharmacokinetics, studies of comparative pharmacokinetics and bioequivalence is the development of an analytical method that allows you to determine the investigated substances in human plasma. There are currently no published methods for the determination of atazanavir and ritonavir in human plasma using high performance liquid chromatography with mass selective detection using a single quadrupole mass detector. In this article presents the development and validation of a method for the determination of atazanavir and ritonavir in blood plasma after sample preparation by the method of protein precipitation. Aim. The aim of the study is to develop a method for the quantitative determination of atazanavir and ritonavir in human plasma by HPLC with mass spectrometric detection for performing the analytical part of pharmacokinetic studies. Materials and methods. Determination of atazanavir and ritonavir in human plasma by HPLC with mass spectrometric detection. A sample was prepared using protein deposition. Results and discussion. The method was validated of selectivity, matrix effect, calibration curve, accuracy, precision, limit of quantification, carry-over effect and sample stability. Conclusion. The method of the determination of atazanavir and ritonavir in human plasma was developed and validated by HPLC-MS. The analytical range of the was 50.0–10000.0 ng/mL in plasma for atazanavir and 10.0–2500.0 ng/mL in plasma for ritonavir. Method could be applied to determination of atazanavir and ritonavir in plasma for PK and BE studies. © Komarov T. N., Shohin I. E., Miskiv O. A., Bogdanova D. S., Aleshina A. V., Medvedev Yu. V., Bagaeva N. S., 2020.