Obsessive-compulsive disorder（OCD）is a heterogeneous disease in terms of manner of onset, dimension of symptoms, and responses to psychological or pharmacological treatments. This paper groups cases of OCD into “effective”and “ineffective”types, based on their responses to exposure and response prevention（ERP）. In the next phase, cases in the “effective”category were further broken down into Type A,characterized as readily responding to ERP, and Type B, characterized as not readily responding to ERP.
 Factors associated with Type B include: 1）below-average intelligence, 2）co-morbidity of other mental disorders, 3）insufficient recognition of irrationality of OCD symptoms, 4）significant difficulties in daily life, 5）insufficient motivation to follow through with ERP,and 6）other personal problems. This paper discusses possible strategies for addressing these factors, and thereby increasing the potential effectiveness of ERP.
 Next, this paper describes the characteristics and treatment of obsessional slowness as a typical type for which ERP is ineffective.
 Finally,this paper examines the process of distinguishing between OCD and other mental disorders that do not respond to ERP in spite of showing OC symptoms.