We assessed the nutritional strategy of true morels (genus Morchella) collected in 2003 and 2004 in Oregon and Alaska, 1 or 2 y after forest fires. We hypothesized that the patterns of stable isotopes (d13C and d15N) in the sporocarps would match those of saprotrophic fungi and that radiocarbon (D14C) analyses would indicate that Morchella was assimilating old carbon not current-year photosynthate. We compared radiocarbon and stable isotopes in Morchella with values from concurrently collected foliage, the ectomycorrhizal Geopyxis carbonaria (Alb. & Schwein.) Sacc., the saprotrophic Plicaria endocarpoides (Berk.) Rifai, and with literature to determine isotopic values for ectomycorrhizal or saprotrophic fungi. Geopyxis, Plicaria and Morchella, respectively, were 3 parts per thousand, 5 parts per thousand and 6 parts per thousand higher in 13C than foliage and 5 parts per thousand, 7 parts per thousand and 7 parts per thousand higher in 15N. High 15N enrichment in Morchella indicated that recent litter was not the primary source for Morchella nitrogen, and similar 13C and 15N enrichments to Plicaria suggest that Morchella assimilates its carbon and nitrogen from the same source pool as this saprotrophic fungus. From radiocarbon analyses Morchella averaged 11 ± 6 y old (n = 19), Plicaria averaged 17 ±5 y old (n = 3), foliage averaged 1 ±2 y old (n = 8) and Geopyxis (n = 1) resembled foliage in D14C. We conclude that morels fruiting in post-fire environments in our study assimilated old carbon and were saprotrophic. © 2016 by the Mycological Society of America.