It is not easy to become a doctor in the United States. Students must attend a college or university and do well in their studies. Students who want to become doctors usually study large amounts of biology and chemistry in college. Some students work for a year or two in a medical or research job before they attempt to enter medical school. Once in medical school, students spend their first two years mainly in classroom study. They learn about the body and all its systems. They also begin studying how to recognize and treat disease. By the third year, students begin working with patients in hospitals. Experienced doctors who have treated many patients guide them as they work. During the fourth year, students begin applying to programs in hospitals for the additional training they will need after medical school. Competition to work at a top hospital can be fierce.