The cultivation of a normal (P2) and a sporeless strain (Sp2) of Pleurotusostreatus on aspen wood shavings supplemented with and without whey was investigated. Whey-containing substrate was susceptible to mold contamination and yield of mushrooms was reduced. Yield on aspen shavings per se was low, 11-15% of original substrate). Yield of Sp2 was higher than that of P2. However the mushrooms of the Sp2 had a very high stem to cap ratio; the stem was more than two and a half times tougher than the cap. Mushrooms grown from whey-containing substrate were more tender in texture and had a higher nitrogen content than those from the water-soaked substrate.