Microdialysis is a non invasive technique, with new applications in dermatological research. The aim of this work was to establish a process which permits to microdialysre, in vitro and in vivo, different lipophilic chemicals [5- and 8-methoxypsoralen (5-MOP, 8-MOP), trimethylpsoralen (TMP)], usually used in skin therapy. The studied parameters were perfusion rate (P.R.), relative recovery (R.R.), equilibrium timing (E.T.).The equipment was composed of a CMA/100 x Microinjection Pump, two types of CMA/20 x Microdialysis probes (membrane length of 10 mm, cut off of 20 and 100 kDa). The perfusate was a phosphate buffer, 0.06 M, pH 7.4. The psoralen dialysates were assessed by High Performance Liquid Chromatography with a fluorimetric detection. Subsequent relative recovery were evaluated at P.R. of 1, 2, 3, 5 and 7.5 μL/min.The R.R. were in a range of 7 to 18% for 5-MOP (logKp = 2.00), and in a range of 17 to 35% for 8-MOP (logKp = 1.93) in relation with decreasing P.R. from 7.5 to 1 μL/min, using 20 kDa membranes. The R.R. were increased by using 100 kDa membranes. The E.T. increased for both drugs (from 1 to 3 hours) with decreasing P.R.. TMP (logKp = 3.14) was never detectable in any experimental conditions.These results, in vitro, seem to be promising for future works, in vivo, for exploring the polarity effect on molecular diffusion in the skin. But it was demonstrated that microdialysis is usable for moderate lipophilic drugs but not for strongly lipophilic ones, with the materials actually available.