An increased proliferation of hybridomas is induced by a polyamine derivative molecule, CEGABA (carboxyethyl gamma-aminobutyric acid). The effects of CEGABA and CR-ECGS (endothelial cell growth supplement) on hybridoma growth are similar. However, both factors are less efficient than HECS (human endothelial culture supernatant) in inducing hybridoma growth through all the steps of hybridoma production, including: recovery after fusion, cloning, and proliferation.