Abstract: Potassium chloride intravenous injection is used in suicide attempts and lethal procedures for state-sanctioned punishment. Owing to its relatively high concentrations in hemolyzed blood (25–80 mM) compared to serum (about 4 mM), it is difficult to conclude potassium poisoning by postmortem analysis of biologic samples. A 41-year-man was found dead with an injection sign on his foot and a syringe close to the corpse. No particular signs were noted during the autopsy. Blood, bile, and urine were submitted to xenobiotic screening procedures used in the laboratory. Syringe content was found positive to potassium ions. Blood potassium concentration was determined by ion-selective electrode measurement (range 3.0–150 mM). Blood was found positive for diazepam at therapeutic level. Potassium concentration was 160.0 (cardiac) and 87.3 mM (femoral blood). Our results show that potassium concentration was significantly higher in heart blood in a suicide case. Hence, the general issue of considering potassium poisoning hardly demonstrable by toxicology needs to be questioned and thoroughly studied.