LC-UV and LC-MS methods have been developed which permit the analysis of parthenolide in different Mexican/US feverfew samples and commercial products. The study was undertaken to confirm the presence of parthenolide in Mexican plant samples and its comparison with US feverfew samples. The best results were obtained with a Phenomenex Luna C18 (2) column using gradient mobile phase of water and acetonitrile:methanol (9 : 1). Elution was run at a flow rate of 1.0 mL per min and ultraviolet detection at 210 nm. The results obtained using LC-UV were comparable to those obtained using LC-MS. Parthenolide was detected in all the samples analyzed and is the major chemical constituent of feverfew. The samples collected in Oaxaca, Mexico (0.28%) and Puebla, Mexico (0.25%) showed the highest content of parthenolide. All Parthenium samples were also examined under light and fluorescent microscopy.