In this paper we introduce the work done to define a framework for requirements and architectural understanding in biomedical grid computing systems. A set of core requirements for biomedical grids have been identified on the basis of our experience in the analysis and development of several biomedical and other grid systems including the National Cancer Institute 's Early Detection Research Network (EDRN) in the US and the National Cancer Research Institute (NCRI) Platform in the UK. The requirements have been specified taking into account different points of view and are intended as a core set that can be extended on the basis of project specific aspects. These are also mapped to existing architectures of biomedical grid systems, and their constituent components. Such a framework is intended as a guide for equipping developers with conceptual tools to avoid costly mistakes when architecting biomedical grid systems.