Polyethylenimine is an amino-based hydrophilic polymer. Polyethyleneimine are used in the cell culture of weakly anchoring cells to increase attachment. Due to the fact that it is a complex mixture of polymers with different molecular weight it is very hard to obtain a single sharp peak for this compound. Polyethylenimine was analyzed on a Promix MP column. The method can be used for quantitation of polyethyleneimines in plasma, blood, saliva and other biological fluids. ELSD and LC/MS methods can be employed for detection.