Abstract Treatment of poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVdF) with hot aqueous solutions of potassium hydroxide resulted in large increases in adhesion. With PVF, the addition of small quantities of tetrabutylammonium bromide to an aqueous solution or the replacement of an aqueous with an alcoholic solution resulted in much more rapid treatment under a given set of conditions. Effective treatments of just 30 and 10s were developed for PVF and PVdF, respectively. Substantial changes in surface chemistry were observed using XPS for most of the pretreatment conditions used; the changes were mainly in the form of defluorination plus introduction of oxygen. The changes were most marked for PVdF treated with solutions containing a small amount of TBAB. Elimination reactions are likely to be of particular importance with PVdF, a view supported by the existence of CC and CC bonds. Substantial chemical modification of PVF did not necessarily result in large increases in adhesion. This is attributed to the chemical modification of a weak boundary layer without its removal.