Clobetasol-17-propionate (CP) was a kind gift from GlaxoSmithKline, Turkey. Lecithin (Lipoid S45) was purchased from Lipoid AG (Ludwigshafen, Germany) and chitosan (Chitoclear FG, specifications: deacetylation degree 95%, viscosity 93 cP for 1% w/v solution in 1% v/v acetic acid) for nanoparticle preparation was from Primex (Haugesund, Norway). Chitosan was used without further purification for nanoparticle preparation. Medium molecular weight chitosan (specifications: MW 190–310 kDa, deacetylation degree 75–85%, viscosity 200–800 cP for 1% w/v solution in 1% v/v acetic acid) for the preparation of gel formulation was obtained from Sigma, USA. Polyethylene glycol 400 (PEG-400) was provided from Merck, Germany. All other chemicals were of analytical grade.