We report at first on two old and large planetary nebulae (PN) of which central stars could satisfy the Ritter's criteria (1986) for being precataclysmic binaries: LoTr5 and Abell 35. Both nebulae have probably been ejected as a consequence of common-envelope evolution. A model of cataclysmic binary (CB) for the central star of Abell 35 has been tentatively attempted by Acker and Jasniewicz (1990). The nucleus of LoTr5 is a triple star (Jasniewicz et al., 1987; Malasan et al., 1991): action of a third body on the separation of the close binary could make this binary evolve into a CB (see Mazeh and Shaham, 1979). We report at second on the similarity between the spectrum of the central star of the extended PN HFG1 with that of a CB (Acker and Stenholm, 1990). The PN cited above could be fundamental objects just at the transition between the stage PN and the stage CB.