The trial will be a double two period (visit) blind cross-over trial with one arm dronabinol 10 mg one arm a placebo control. The order of doses and placebo will be randomized with the restriction that half of the subjects will receive each order. This counterbalances possible visit effects or learning effects associated with the visits. The use of an oral cannabis analog is not equivalent to smoking as the onset of action is slower. This is why people who use dronabinol for chronic pain prefer to smoke cannabis. There is no "high" associated with dronabinol. However, the active ingredients are the same, THC, which will have similar effects on the cannabinoid 1 receptor. Ethically, we did not feel we could ask people to smoke cannabis on one day of study. Subjects will present to the GCRC at 5:00 p.m. They will abstain from use of cannabis overnight. The following morning, at 8:00 a.m., the subject will provide a urine sample for a toxicology screen and a blood sample for quantitative THC levels. They will then be administered either 10 mg of dronabinol or an identical placebo on an alternate day. The subject will then have a baseline assessment of clinical positive and negative symptoms measured by the Brief Psychiatric Rating Scale (BPRS). The majority (70-90%) of people with schizophrenia smoke cigarettes. Thus, it is likely that in this population that smokes cannabis, 100% will also be cigarette smokers. The effects of nicotine via cigarette smoking on the endophenotypes studied is an acute effect, with a peak at about 5 minutes. To preclude nicotine effects on endophenotypes, we have the patient not smoke for 20 minutes prior to and during testing. Nicotine is quickly removed from the body when inhaled and its effects wear off within 20 minutes. Two hours after administration, the subject will perform the following tests: P50 auditory evoked potential- the recording will consist of the presentation of 5 sets of 16 click pairs with an intrapair interval of 500 ms heard through headphones with a 3-minute rest between sets. Brain wave responses will be recorded; neurocognitive assessment-the California Verbal Learning Test will measure verbal memory and the Stroop will measure inhibition; clinical symptom assessment- The BPRS will again be administered measure positive and negative symptoms; and a blood sample will be collected for quantitative THC levels. They will then be escorted by a Clinical Research Center nurse over to a laboratory at Colorado Psychiatric Hospital to perform smooth pursuit eye movements In performing smooth pursuit eye movements, they will watch a dot moving across a computer screen while infrared sensors that are placed just in front of their eyes record their eye movements. Each subject performs 3 trials of one minute each, with 2 minutes rest between each recording. Subjects will be reassessed by the BPRS for drug exacerbation of symptoms, will have vitals, will be checked for adverse effects, will perform a sobriety test (the standard test used in roadside testing i.e. walking a straight line and finger to nose testing) which will be assessed by Dr. Olincy, who is experienced in assessing sobriety, to assure that the patient is not acutely intoxicated and able to perform normal functions that require coordination. If they fail the sobriety test, they will be asked to remain in the (General Clinical Research Center (GCRC) until they can pass the sobriety test. Otherwise, they will then will be discharged at 5:00 p.m. Transportation to and from the GCRC will be by a provided cab service. Subjects will be randomized in blocks of 4 or 6 to the order in which they receive placebo or dronabinol. The interval between the two days of testing will be 1 week.