Forty consenting schizophrenic patients, 18-60 years old, physically healthy, with more than 2 years of illness in a stable condition (no gross changes in clinical presentation in the last 6 months as judged by the patient's psychiatrist) and presenting negative and cognitive symptoms (as judged by the patient's psychiatrist along with score in at least 3 items of the PANSS negative subscale =4 points, while items of the PANSS positive subscale scored = 3 points). These patients will be recruited into the study over two years.