 Background: There is a paucity of data as to the effect of methylphenidate MPH on young adults who do not have attention deficit hyperactivity disorder ADHD. The existing data is equivocal and focuses on neuropsychological functions that are not always relevant to the clinical aspects of attention. Objective: To determine the effect of MPH on a diagnostic continuous performance task that assesses attention per se TOVA and on a decision making test Modified Gamble Decision Test in young, healthy adults. Methods: Fifty young adults, men and women ages 20-30, without ADHD, learning disabilities, history of past or present use of MPH or other psychotropic drugs, will be eligible to participate. Design: The experiment will be conducted in 2 sessions, the first lasting 3.5 hours and the second 2.5 hours in a randomized, double-blind prospective design. In the first session, the subjects will be screened for ADHD past and present, major psychiatric diagnosis depression, anxiety, etc, use of MPH in the past, psychotropic medications or recreational drugs and any other chronic illness; urine will be tested for beta-hCG to rule out pregnancy. Blood pressure and heart rate will be measured. The participants will then be given either placebo or MPH 15-20 mg and after 90 minutes will proceed to complete the TOVA that lasts 22 minutes and Modified Gamble-Decision Test 15 minutes. Before taking the pill and prior to the testing, the subjects will complete the Visual Analogue Scale VAS which quantifies their subjective feelings regarding present mental and emotional state. In the second session, 2 weeks later, blood pressure and heart will be measured and the VAS completed prior to and 90 minutes after taking the tablet. The subjects then undergo the TOVA and Modified Gamble-Decision Test. Data Analysis: will be performed using the paired t-tests for parametric variables and one way ANOVA with repeated measurements. Significance: Results of this study are important since MPH is used and abused by healthy students as a study aid although its objective effects in normal young adults are not well delineated 