In this work the agronomic viability of substrates based on spents of Agaricus bisporus (J.E.Lange) Imbach) (SAS) and Pleurotus ostreatus (Jacq.) P. Kumm. (SPS) was studied. In addition to the commercial substrate used as reference, six different treatments were considered. In this experiment, SPS and SAS were mixed in different ratios (from 6,000 g and 0 g, respectively, up to 3,000 g and 3,000 g, respectively). SAS was subjected to a heat treatment in a growing room ("cook out") and then to a maturation treatment which consisted of a controlled recomposting process in growing rooms. SPS was subjected to a pasteurizing heat treatment (60 °C - 65 °C, 8 h) and progressive decrease for at least 15 h to a "spawning" temperature (25 °C).