Flector plaster is a new transdermal delivery system medicated with diclofenac hydroxyethylpyrrolidine salt, an NSAID which seems to possess suitable physiochemical properties for easy release by the plaster matrix for percutaneous absorption. The paper deals with local tolerability and pharmacokinetic (percutaneous absorption) studies carried out both on animals and on volunteers. The results obtained in the safety studies demonstrate the absence of local skin reactions and of sensitization phenomena. The kinetic evidence, obtained at the steady-state, reveals a profile typical of a sustained-release formulation, able to maintain constant plasma levels of the drug up to the next application (12 h). The amount of drug bioavailable for targeting the sites of action is effectively lower than via the oral route, however the estimated absorbed dose of 5-10 mg per application appears to be adequate for the foreseen therapeutic use, taking into account the great advantage in having no undesirable side effects.