Wood chips from four commercial hardwood sawmills were screened with 10 US standard sieves (4-0.21 mm) to assess particle size distributions. 96-98% of wood chips were < 4 mm while 95-99% of particles were > 0.21 mm. The majority (mean = 64.5%) of wood chips passed through US standard sieve size 14 (< 1.4 mm). Shiitake (Lentinula edodes) was grown in three crops to determine the effect of four particle size classes (1 = 2.8-4 mm; 2 = 1.7-2.8 mm; 3 = 0.85-1.7 mm; 4 = < 0.85 mm) on mushroom yield. Yields from substrates prepared with wood chips from class 4 (< 0.85 mm) were lower by 27.7%, 12.4% and 2% (mean = 14.9%) for Crops I, II, and III, respectively, when compared to controls. Profiling of wood chips may help growers optimize their production media and reduce production costs.