Discrimination in carbon and nitrogen isotopes of decomposing plant litter in the northern Chihuahuan Desert was determined for a 5-year period. Factors influencing isotopic change were assessed from inter-species comparisons of litter chemistry, mass loss patterns, and isotope values of associated soil. Average delta¹⁵N litter values of buried roots increased 1.2 and 2.6‰ for Big Blue Stem (Schizachyrium gerardi, grass) and Varital (Drypetes glauca, hardwood) during the study, respectively. Small but inconsistent variations were observed for Slash Pine (Pinus elliotii, conifer) roots. Average delta¹⁵N values of wooden dowels from Ramin (Gonystlylus bancanus, hardwood) increased ca. 2.0‰ during years 1–4, and then decreased slightly during year 5. Changes in delta¹⁵N litter were independent of N content, and may reflect microbial fractionation or preferential retention of ¹⁵N enriched substrates. Surprisingly, there was no clear relationship between litter N dynamics and C/N ratios. There were no discernable changes in delta¹³C litter values for Gonystlylus bancanus and Pinus elliotii. Average delta¹³C litter values for Schizachyrium gerardi decreased ~2.0‰ during years 0–2 and then increased slightly. In contrast, average delta¹³C litter values for Drypetes glauca increased ~0.5‰ from years 0–1 then remained relatively constant until decreasing slightly in year 5. Delta¹³C litter discrimination may have been masked by interfering delta¹³C fractionations or feedbacks between decomposers and litter chemistry. Our data indicate that isotopic discrimination is characteristic of early litter decay stages. These results may highlight aspects of isotope discrimination and nutrient cycling unique to arid land environments. Additional studies will be needed to confirm this.