A liquid developer composition for rendering visible electrostatically charged areas. The composition contains in an electrically insulating non-polar carrier liquid having a volume resistivity of at least 10.sup.9 ohm.cm and a dielectric constant less than 3, dispersed coloring matter acting as toner particles and at least one onium salt polymer including recurring units incorporating an onium group together with an anion. The anion has at least one of the following characteristics:(1) contains a negatively charged atom or group of atoms which is sterically embraced by at least two non-ionic substituents containing at least 4 C atoms;(2) contains a negatively charged atom which is sterically embraced by at least 4 atoms selected from the group consisting of oxygen and halogen;(3) contains a negatively charged atom or group of atoms the negative charge of which is delocalized over other atoms linked to said atom or group of atoms;(4) is a radical anion,whereby the onium salt polymer is adsorbed with a net positive charge on the toner particles. An illustrative onium salt polymer species is a copolymer of isobutyl methacrylate, stearyl methacrylate and dimethylaminoethyl methacrylate that has been quaternized with methyl iodide and of which the iodide anions have been replaced by tetraphenyl boride anions.