  Five planetary nebulae are known to show hydrogen-poor material near the
central star. In the case of A58, this gas was ejected following a late thermal
pulse similar to Sakurai's Object. In this paper I will review these five
objects. One of them, IRAS 18333$-$2357, may not be a true PN. I will show that
there is a strong case for a relation to the [WC] stars and their relatives,
the weak emission-line stars. The surface abundances of the [WC] stars are
explained via diffuse overshoot into the helium layer. The hydrogen-poor PNe do
not support this: their abundances indicate a change of abundance with depth in
the helium layer. A short-lived phase of very high mass loss, the r-AGB, is
indicated. Sakurai's Object may be at the start of such a phase, and may evolve
to very low stellar temperatures.
