This paper presents the combined application of flow injection (FI), on-line film deposition, electrochemical stripping, and electrochemical quartz crystal microgravimetry (EQCM) detection to the analysis of compound semiconductor films. The combined FI–EQCM technique and setup were first tested with experiments involving cadmium and silver deposition and the stripping of these metals. They were then used for the analysis of films comprising CdSe, free Cd, and free Se. Selective stripping of these film components with concomitant monitoring of the frequency changes in the EQCM detector facilitated compositional assay of such films. Data are presented for films electrosynthesized over a range of potentials.