Objectives: Estimation of post mortem interval (PMI) remains one of the most difficult challenges to a medicolegal expert. Postmortem biochemical changes may provide chemical markers to help more accurate determination of the postmortem interval. Obtaining postmortem blood samples is a simple and non invasive procedure. The purpose of the study was first, to  compare time dependent changes in  concentrations of   NADH, ammonia and uric acid   versus morphological  changes of white blood cells of in-vitro stored and postmortem blood samples for each time points 0, 12,24,48and72h. Second to find out an    objective and quantitative standard for the estimation of postmortem interval. Materials and Methods: This study was carried out on blood samples collected from 30 healthy volunteers (group I) and 30 medicolegal autopsy cases (group II). Changes in concentration of NADH, ammonia and uric acid were recorded at (0, 12, 24, 48 and 72h) of postmortem and storage periods. Also, blood films have been examined using a light microscope after staining with Giemsa stain to observe and compare morphological changes of white blood cells at the previous time intervals. Results: Concentrations of NADH, ammonia were significantly increased with time in (group II) while, uric acid showed no significance increase between both groups for the whole 72 hours. Also, degenerative morphological changes in white blood cells were in the form of pyknosis, cytoplasmic and nuclear vacuolation, nuclear fragmentation and disintegration. These changes were the same in both groups all over the time points of the study. Conclusion: From the previous results, it can be concluded that there were time dependent changes in NADH and ammonia levels, degenerative morphological changes of white blood cells. Also, there was a strong positive correlation between concentrations of   plasma NADH and neutrophilic changes all over the time points of the study in the medicolegal autopsy cases.