A method for development of a liquid pharmaceutical composition to be applied as a foam to the skin, wherein the foamable liquid composition contains at least one solvent, at least one pharmaceutical active ingredient, and at least one phospholipidic foaming agent, characterized in that a) the phospholipid foaming agent is such a phospholipidic foaming agent, which is isolated from soybeans and contains phosphatidylcholine in a concentration between 50 % by weight and 95 % by weight, whereby said phosphatidylcholine has an acid number of at most 10, a peroxide number of at most 10, and an oil concentration of at most 6 % by weight, relative to the dry weight of the phosphatidylcholine, that b) the foam volume and the foam stability of the foam are determined by a SITA measurement method as being described by the examples, whereby the foam is created without the use of a propellant and whereby using the SITA measurement method 250 ml of the liquid composition are foamed with a rotor speed of 2000 rpm during five rotor cycles each of which have a duration of 20 seconds and a pause of 15 seconds between each rotor cycle and whereby the foam volume is measured every 50 seconds by means of the needle detectors over a period of 35 minutes, and that c) in the liquid composition the at least one foaming agent, the at least one solvent and the at least one pharmaceutical active ingredient are varied so long in regard to their chemical nature and/or concentration until the foam created by the SITA measurement method has d) a foam density between 0,05 g/ml and 0,8 g/ml, e) a foam volume between 450 and 1400 ml, and f) such a foam stability that the foam still has, after a dwell time of up to five minutes, at least 50% of the foam volume that was originally present immediately after the creation of the foam. a) the phospholipid foaming agent is such a phospholipidic foaming agent, which is isolated from soybeans and contains phosphatidylcholine in a concentration between 50 % by weight and 95 % by weight, whereby said phosphatidylcholine has an acid number of at most 10, a peroxide number of at most 10, and an oil concentration of at most 6 % by weight, relative to the dry weight of the phosphatidylcholine, that b) the foam volume and the foam stability of the foam are determined by a SITA measurement method as being described by the examples, whereby the foam is created without the use of a propellant and whereby using the SITA measurement method 250 ml of the liquid composition are foamed with a rotor speed of 2000 rpm during five rotor cycles each of which have a duration of 20 seconds and a pause of 15 seconds between each rotor cycle and whereby the foam volume is measured every 50 seconds by means of the needle detectors over a period of 35 minutes, and that c) in the liquid composition the at least one foaming agent, the at least one solvent and the at least one pharmaceutical active ingredient are varied so long in regard to their chemical nature and/or concentration until the foam created by the SITA measurement method has d) a foam density between 0,05 g/ml and 0,8 g/ml, e) a foam volume between 450 and 1400 ml, and f) such a foam stability that the foam still has, after a dwell time of up to five minutes, at least 50% of the foam volume that was originally present immediately after the creation of the foam.