The authors present an overview of the process for developing DSM IV which has been characterized by extensive international communication and collaboration and which includes three stages of empirical review: systematic literature reviews, analysis of unpublished data and field trials. Next, they describe in detail recently initiated DSM IV field trials. The field trials will study eleven diagnostic categories which continue to be the focus of much discussion. They include antisocial personality disorder, autism, disruptive disorders, dysthymia, insomnia, mixed anxiety and depression, obsessive-compulsive disorder, posttraumatic stress disorder, schizophrenia, somatoform disorder and substance use disorders. Each field trial compares the DSM III, the DSM III-R, ICD 10 and proposed DSM IV criteria for the disorder in question.