A method based on nuclear magnetic resonance spectroscopy is described for the quantitative determination of polyimethylsiloxane (PMS) in a variety of pharmaceutical preparations. An extraction procedure using deuterochloroform within the sample tube was devised. In the presence of an internal standard, the PMS concentration was determined directly using integrated peak areas, without the necessity of establishing calibration curves. Accurate quantitative results were achieved with sample, containing at least 2mg PMS, extracted from formulations containing greater than 0.5% PMS. The extraction procedure and nmr assay were both more efficient and convenient than the B.P.C. method.