Crayfish are major functional components of Ozark Plateau stream ecosystems and dominate the invertebrate biomass.  However, crayfish are absent near some lead/zinc mines in the Black River watershed of southeast Missouri due to extensive metal contamination of water, sediments and detritus.  Previous in-situ cage studies with juvenile crayfish demonstrated an inverse relationship between survival and metal concentrations.  We conducted a 56-d laboratory study to determine the effects of a mixture of metals (cobalt, nickel, zinc, lead and cadmium) on the survival and growth of woodland crayfish (Orconectes hylas), and microbial decomposition rates of three leaf species:  cottonwood (Populus deltoids); American sycamore (Platanus occidentalis), and black willow (Salix nigra).  Survival of crayfish was reduced at the high metal treatment and percent weight gain in crayfish decreased with increasing metal concentrations.  Weight loss of leaves from only microbial decomposition was greatest for cottonwood>willow>sycamore and the weight loss of all species was less with increasing metal concentrations.  Weight loss of sycamore leaves was greater with crayfish than without crayfish. These results indicate that crayfish are impacted by metals in the Black River watershed, and that loss of crayfish may have negative effects on leaf decomposition and other functional processes of Ozark streams.