A mixture of apple pomace and sawdust was tested as a substrate for production of shiitake [Lentinula edodes (Berk.) Pegler] and oyster mushroom [Pleurotus ostreatus (Jacq. ex Fr.) Kummer and P. sajor-caju (Fr.) Sing.] on synthetic logs. MyCelia grew faster and more densely in logs containing apple pomace than in sawdust alone. Five shiitake isolates and two Pleurotus spp. produced higher fresh weights on a mixture of equal parts (by weight) of apple pomace and sawdust than on either substrate alone. An alternative substrate based on sawdust, millet (Panicum miliaceum L.), and wheat (Triticum aestivum L.), bran gave almost identical overall yield as pomace-sawdust medium, but there was a significant differential effect of the substrates on yield of the two tested shiitake isolates. Analyses and experiments in vitro suggested that optimal N levels provided by apple pomace account in part for its effectiveness.