Psychobiology (sometimes called biopsychology) is the study of behavior in a biological context. Based on the theory that most behavior is the result of some action of the nervous system, much of psychobiology is focused on the study of the brain.
With (slightly) less jargon, psychobiologists try to figure out what internal stuff is responsible for or related to what external stuff. For example, a typical psychobiology experiment could involve figuring out whether any neurochemical changes consistently precede bouts of depression. The role of evolutionary history in human behavior also commonly comes up in psychobiology research (e.g., all that research about the relationship of waist-to-hip ratio, fertility, and perceived attractiveness).
Psychobiology students are expected to be familiar with high level psychological theory, but are not required to learn how to counsel people. They learn biological research methods and theory, and organic chemistry. It's a great field for people who find psychology too wishy-washy, or who are interested in humans and biology but don't want to go to medical school.
To find out more, /msg me, or see any textbook with a title like, "Brain and Behavior" or, "The Physiology of Behavior."