Class of 2005 Abstract / Objective: The goal of this study was to determine the presence of erythro-methylphenidate (erythro-MPH) isomers contained within methylphenidate HCl (Metadate CD®) capsules. Methods: This experiment was conducted at a pharmaceutical manufacturing facility located in Tucson, Arizona. Methylphenidate HCl (MPH) capsules by Celltech Pharmaceuticals, Inc. were analyzed and compared to a reference standard. Thin-layer chromatography (TLC) was the technique used to qualitate the samples. The main outcome measure was the Rf values which were used to determine whether or not the MPH capsules contained erythro-MPH. Results: The study included ten, 20 mg MPH capsules and a reference standard (50 mg strength USP MPH related compound). The Rf value of the reference standard was 0.073 while the Rf value of the MPH samples ranged from 0.42 - 0.85. Conclusion: In this qualitative analysis of MPH capsules, there was no erythro-MPH isomers present in the MPH capsules.