We studied the effects of the presence ofRobiniapseudoacacia L. on decomposition rates and nitrogen mineralization in the forest floor of two northern hardwood stands in western Massachusetts, one with and one without Robinia. Leaves from two hardwood species on the two sites and Robinia leaves were set out in mesh bags on the two sites for a total of 10 treatments. Increased nitrogen concentrations and lower carbon/nitrogen ratios were evident in leaves from the stand with Robinia, but this did not significantly affect rates of decomposition, which were the same for all 10 combinations of species, source, and site. Mineralization was observed only in leaves of Robinia placed on the Robinia stand and in leaves of Acersaccharum Marsh. placed on the stand without Robinia. Carbon/nitrogen ratios of Robinia litter were significantly lower than carbon/nitrogen ratios of Fraxinusamericana L. or Acer litter throughout the experiment. Site of decomposition did not appear to affect carbon/nitrogen ratios as decomposition proceeded.