Grids are a novel class of distributed systems that allow to seamlessly combine multiple resources of heterogeneous servers on the Internet for demanding applications. We deal with the challenging task of programming grid applications which have to meet the requirements of abstraction and interoperability. We present our concept of customizable Higher-Order Components (HOCs) whose parameters may be not only data but also mobile code units. We demonstrate how applications are built by customizing HOCs using code parameters and describe the HOC-SA – a service-oriented architecture for developing grid applications by composing HOCs. We show where HOC-SA ranges in the variety of currently available software component architectures. In presenting our implementation, we explain how HOC-SA exploits modern grid middleware such as the WSRF implementation in the latest Globus Toolkit while hiding its complexity from the user.