This study investigates subject teachers' practical knowledge and teaching behaviour regarding integrated language teaching in the context of vocational education. The emphasis was on the nature of teachers' subject-specific language awareness and how they enact this awareness in their teaching practice. For this purpose, teachers in vocational education were interviewed and observed while teaching. The results reveal that teachers differ in their subject-specific language awareness. Some teachers are unaware of the relation between language and learning, while others are aware of this relation and feel responsible towards their students' language proficiency. Teachers who feel this responsibility stimulate students' active language use and use more advanced interaction strategies to promote students' higher cognitive thinking. The results of this study indicate that raising subject teachers' language awareness needs to be part of activities for teacher professional development.