Commercial polyimide (PI, ‘kapton') and polycarbonate (PC, ‘makrofol') foils have been irradiated with 135 MeV Ar5+and 340 MeV Xe7+ions, respectively, and subsequently boiled in a 5 mole/ltr LiCI solution for different times. The depth distributions of Li diffused into the foils suggest that the doping proceeds via regular diffusion, into both unirradiated bulk and into tracks. Low fluence irradiations appear to lead to a compaction or densification of the polymer matrix. One consequence of this is a decreasing Li uptake with increasing fluence. For higher ion fluences the Li uptakeproportional to track densitybecomes dominant. It is possible to define, to first order, a mean ‘effective track radius’ for the average amount of lithium taken up per track, and this can be shown to be of the order of only an Å. The diffusional behaviour of lithium suggests that tracks in 340 MeV Xe ion irradiated polyimide act as open micropores for diffusing dopants. Conversely, in 135 MeV Ar irradiated PC, the dopant may only access the primary track core by passage through nearby undisturbed polymer target. A characteristic surface effect is the eventual appearance of crater-like profiles associated with the cores of ion tracks at projectile points of entry. These may be partly due to reverse ‘blow-out’ (backwards sputtering) in plumes of dissociated polymeric matter.