Aim. To examine the antihypertensive effect of the synthetic analogue of the endogenous nitric oxide donors in patients with grades 2-3 hypertension and uncomplicated hypertensive crisis (HC). Subjects and methods. The study included 30 male patients aged 35 to 73 years (mean age 55.5±10.8 years). All the patients had grades 2-3 essential or secondary hypertension. Thirteen (43.3%) patients were observed to have signs of HC; 17 (56.7%) patients had persistent blood pressure (BP) elevation. A dinitrosyl iron complex was injected in a dose of 1.5 or 3 mg per kg of body weight. The purpose of its administration was to lower BP by at least 20% of its baseline level. Results. No significant side effects associated with the administration of the test drug were recorded when the clinical trial protocol was implemented. All the patients reported fever and facial hyperemia during and 10-20 minutes after injection. They all (100%) showed efficient blood pressure reduction of at least 20% of the baseline level. Blood pressure changes were similar when the agent was administered in doses of 1.5 or 3 mg/kg. At 6-8 minutes after the drug was injected, there was a maximal decrease in blood pressure, then its gradual rise and stabilization at a lower level than the baseline one within the following 8 hours. There were no significant differences in the magnitude of a blood pressure reduction after administration of 1.5 and 3 mg/kg. Conclusion. The findings suggest that the dinitrosyl iron complex is highly effective in treating uncomplicated HC. The antihypertensive effect of the drug persists for 8 hours after its injection, which is very important during prehospital therapy. The drug is well tolerated by patients and causes an insignificant number of side effects.