An important component of forensic fiber analysis involves dye identification and comparison. UV/visible-based approaches to dye analysis are frequently used yet they are unable to distinguish between two structurally similar dyes. The current study used LC-MS to analyze seven pairs of commercial dyes that have similar UV/visible absorption profiles and absorption maxima within 5 nm. All seven pairs were examined by UV/visible spectroscopy and by LC-MS. Two pairs of cotton fibers that were indistinguishable with UV/visible spectroscopy were differentiated by LC-MS. The findings suggest the utility of using LC-MS for distinguishing between known and questioned fibers in cases where the dyes are different at the molecular level. If LC-MS also fails to distinguish fibers based on their dye content, it is recommended that the analysis be extended to the use of LC-MS/MS or MS/MS of the extracted dye mixture. Figures, references