Chemical abundances in ionised nebulae suffer from the abundance discrepancy problem: abundances from recombination lines are always higher than those derived from collisionally excited lines. In planetary, nebulae, the discrepancy is typically a factor of 2-3 but occasionally reaches orders of magnitude. Recent work has linked extreme abundance discrepancies in planetary nebulae with close binary central stars, with almost all PNe with close binary central stars and a measured abundance discrepancy having an extreme value. This may indicate that a nova-like event ejects hydrogen-deficient material into the nebula. I will discuss recent observations and ongoing work to confirm this link.