Manufacturing environments are characterized by a multitude of heterogeneous devices, networks, specific protocols and applications. Therefore, static structures, close coupling and vendor-specific solutions have been established over decades. To increase flexibility and interoperability we introduce a service-oriented middleware approach in form of an integration layer between shopfloor equipment and enterprise applications. The integration layer addresses the actual capabilities and data flows on the field and control layer individually. It offers core services that are applicable in several manufacturing domains. We describe a detailed case study to discuss pros and cons of a SOA approach in manufacturing systems and to show the feasibility of our approach.