The pig's palatal mucosa is used as a simple model of in vitro vertical diffusion to study the permeation of different dosage forms of nicotine. Nicotine-loaded microspheres as well as solutions are tested and some parameters of diffusion determined (fluxes, lag-time, etc.). The nicotine fluxes of solutions and microspheres do not differ significantly, except in the case of nicotine base formulations. However, the lag-time of microspheres formulations seems to be half the lag-time of solutions. The swelling of microspheres provoking a dehydration of the mucosa, as well as the high concentration of nicotine in microspheres directly in contact with the mucosa, seem to explain this difference of lag-time.