Description:The purpose of this study was to examine the metabolic profiles of mayfly (Centroptilum triangulifer) larvae subjected to a thermal challenge. This species is unusual in terms of its ease of culture, and its suitability as a laboratory test organism. Studies complementary to this metabolic study have focused on thermal effects on metabolic rates (respiration) and gene expression patterns in this species and do not support Prtners oxygen limitation paradigm. Our purpose here was to examine how an environmentally realistic thermal challenge affects the physiology of this organism.