Endotoxin is heat-stable lip polysaccharide (LPS) present in the outer membrane of the cell wall of Gram-negative bacteria. All parenteral preparations, as well as tissue implants, must be with no pyrogenic level of endotoxin or other related materials because of their associated health hazards and serious clinical effects. Accordingly, detection and limiting endotoxin in various pharmaceutical and biological products represent crucial issues. Rabbit pyrogen test (RPT) and Limulus Amebocyte Lysate (LAL) test are two methods used for endotoxin detection and quantification. Endotoxin detection is one of the most critical quality control tests required by the Food and Drug Administration (FDA) for all parenteral drugs in their final stage. Both in vitro LAL test and in vivo RPT can complement and reinforce each other but in certain cases, they are not interchangeable and they together provide a comprehensive picture of any potential contamination whether by endotoxin or any other pyrogenic matters.