The reverse micelle-based microemulsion was proposed as a vector for the transdermal delivery of propranolol. Soya-lecithin forms reverse micelle in iso-octane with increased solubilizing potential. The lecithin/iso-octane system was studied for the nature of solubilized water, the effect of added water on viscosity, and drug-micelle interaction. The amount and nature of solubilized water was investigated by spectroscopic methods using potassium nitrate as the polarity probe. With increasing water content the viscosity of the system was found to increase. And at a molar ratio (R) = 3, the system showed gel-like consistency (8.1 X 10(3) poise). The polarity probe study suggested the difference in environment of solubilized water as compared with the bulk water. The permeability rate of propranolol contained in the water/lecithin/iso-octane system was calculated to be 1212.0 mug h cm-2 while in the case of petrolatum jelly it was recorded to be 122.8 mug h-1 cm-2.