Teacher attitudes toward the mainstreaming of students with handicaps is a topic of international concern. Although as a social and educational policy, mainstreaming has been attempted with greatly varying degrees of success in the United States and elsewhere for the past ten years, very little empirical evidence existed to give support to such a policy. The author's study, conducted in Spain prior to a nationwide effort to integrate children with handicaps into regular classrooms, indicates that the success or failure of such programs is crucially linked to teachers' willingness to accept the concept of mainstreaming. This study examines teacher attitudes and related variables about mainstreaming before its inception, and resolves some of the difficulties that have been experienced with its implementation. This is an extremely important document for educators and others involved with handicapped children.