Each year 730,000 Americans experience a stroke. Forty percent are left with significant paralysis of one arm. Certain types of physical therapy, for example constraint induced movement therapy (CIMT), have been shown to be effective in improving arm function. However, for most subjects, improvement is modest. In this trial, we test two approaches that may increase the amount of improvement achieved: 1) distributing treatment over a greater amount of time; and 2) adding a drug, d-cycloserine, which theoretically enhances the molecular mechanisms of learning.