Progesterone was determined in commercial pharmaceutical formulations and experimental micellar systems by means of two analytical methods based on liquid chromatography and derivative spectrophotometry. The chromatographic analysis, with ultraviolet detection at 245 nm, was carried out on a C8 column using a mobile phase composed of 2-propanol and a pH 2.5, 30 mM phosphate buffer. Derivative spectrophotometry (DS) used the difference between the values of the first derivative at 227.2 and 253.6 nm. Both methods require only a simple extraction procedure of progesterone from the formulations before analysis. The high-performance liquid chromatography (HPLC) procedure allows for the quantitative determination of progesterone in all pharmaceutical formulations tested (oily and alcoholic injectable solutions, gel preparations and soft capsules) and also of the newly-developed polymeric micellar system. On the contrary, the derivative spectrophotometric method is not suitable for the pharmaceutical formulation containing estradiol and for the new micellar systems. The results obtained with the two methods are in good agreement and always satisfactory in terms of precision and accuracy.