Objectives: Liver, spleen and bone marrow represent the organs with high reticuloendothelial system (RES) activity. This system is composed of cells which play an active role in the defense mechanism. We hypothesized that in patients with AMI, metabolic activity of organs containing RES will be higher than control subjects. Methods: We total 48 subjects consisted of acute myocardial infarction (AMI) patients (n=32, 57짹12 years) within one week and control subjects(n=16, 54.4짹7.2 years). Patients had fasted 6 h before PET acquisitions and blood glucose had to be less than 7 mmol/l before injection of 310–450 MBq (5–7 MBq/kg) of 18F-FDG. The maximum SUV for right carotid artery, ascending and descending aorta, RES system such as liver, spleen, bone marrow, and lung, visceral fat and subcutaneous fat. Bone marrow and spleen uptake analysis on 18F-FDG PET/CT imaging. BMU level was visually evaluated in homogeneous bone areas outside of possible focal uptakes and graded according to liver uptake (1=below liver uptake, 2=corresponding to liver uptake, 3=above liver uptake). Associated focal BMUs were also reported. As semi-quantitative reference, maximum standardized uptake values (SUV) were generated using a region of interest (ROI) on the sacral promontory. The ROI was drawn manually inside the bone area of the sacral promontory using CT data for anatomical location. Performance of 18F-FDG PET diffuse BMU and SUV to detect bone/bone marrow involvement was also assessed. In that case BMU grade 3 and SUV ��� 2.7 were used as positive scan criteria; SU was visually graded according to liver uptake (1=below liver uptake, 2=corresponding to liver uptake, 3=above liver uptake). Results: The maximum SUVs for the liver, bone marrow spleen and lung were higher in patients with AMI to control subjects(p< 0.05). In contrast, the maximum SUVs for subcutaneous fat did not show any significant difference (p>0.05). We compared the SUVs for each organ noted. Conclusions: The maximum SUV for the organs with RES activity were higher in patients with AMI than in control subjects. This could imply that organs with RES cells play an important role in the inflammatory response which can be detected and quantified by the FDG-PET imaging technique. The degree of this response may have a prognostic role in such patients and should be explored further in the future.