The modern observations of the planetary nebulae (PNe) are used to create a new catalogue of He, C, N, O and other element abundances for Galactic and extragalactic PNe. This catalogue is planned to be used for studies of galactic chemical evolution. The inclusion of UV data for PNe from IUE lets us to define more precisely the element abundances. We have used the modern observations of PNe to determine the parameters of nebulae and element abundance in them. The abundances of He, C, N and O in Galactic PNe are compared with those calculated in the model by Marigo [1]. A class of nebulae with low element abundances is picked out. The properties of PNe in the class are considered.