An ex situ bismuth film electrode (BiFE) was used for the electrochemical study of the hormone progesterone. Two peaks were observed by cyclic voltammetry, at -1.68 V and -1.47 V, respectively, associated with the reduction and oxidation reactions of progesterone in 0.1 mol L-1 Britton-Robinson solution at pH 12.0, in agreement with a quasireversible electrode process. In relation to the mechanism, an adsorption-controlled reaction rate with one electron involved in the electrochemical step was observed. Square-wave adsorptive stripping voltammetry was used for the analytical procedures after accumulation of the progesterone for 60 s at -1.0 V. A peak current at -1.63 V related to the reduction of progesterone was obtained, which increased linearly with the hormone concentration in the range of 0.40-7.90 mu mol L-1 (R-2=0.9983). The limit of detection attained was 0.18 mu mol L-1. The method was applied in the determination of progesterone in four pharmaceutical samples with satisfactory results being obtained compared with a spectrophotometric method. (C) 2013 Elsevier Ltd. All rights reserved.