Background. Experimental and first clinical studies suggest that the transplantation of bone marrow derived, or circulating blood progenitor cells, may beneficially affect postinfarction remodelling processes after acute myocardial infarction. Aim. This pilot trial reports investigation of safety and feasibility of autologous bone marrow-derived progenitor cell therapy for faster regeneration of the myocardium after infarction. Methods and results. Four male patients (age range 47-68 years) with the first extensive anterior, ST elevation, acute myocardial infarction (AMI), were treated by primary angioplasty. Bone marrow mononuclear cells were administered by intracoronary infusion 3-5 days after the infarction. Bone marrow was harvested by multiple aspirations from posterior cristae iliacae under general anesthesia, and under aseptic conditions. After that, cells were filtered through stainless steel mesh, centrifuged and resuspended in serum-free culture medium, and 3 hours later infused through the catheter into the infarct-related artery in 8 equal boluses of 20 ml. Myocardial viability in the infarcted area was confirmed by dobutamin stress echocardiography testing and single-photon emission computed tomography (SPECT) 10-14 days after infarction. One patient had early stent thrombosis immediately before cell transplantation, and was treated successfully with second angioplasty. Single average ECG revealed one positive finding at discharge, and 24-hour Holter ECG showed only isolated ventricular ectopic beats during the follow-up period. Early findings in two patients showed significant improvement of left ventricular systolic function 3 months after the infarction. There were no major cardiac events after the transplantation during further follow-up period (30-120 days after infarction). Control SPECT for the detection of ischemia showed significant improvement in myocardial perfusion in two patients 4 months after the infarction. Echocardiographic assessment in these two patients also showed significant improvement of systolic function three months after the infarction. Conclusion. Preliminary results of the study showed that the transplantation of bone marrow-derived progenitor cells into the infarcted area was safe, and feasible, and might improve myocardial function. Further follow-up will show if this treatment is effective in preventing negative remodeling of the left ventricle and reveal potential late adverse events (arrhythmogenicity and propensity for restenosis).