A Grid is computer-based infrastructur that provides dependable, consistent, pervasive access to distributed resources. Built on top of a Grid, a Semantic Grid is a service-oriented infrastructure that provides a range of computation, information and knowledge services. A purpose of a Grid portal is to provide easy and seamless access to Grid heterogeneous resources and services through a Web- based user interface. This paper presents PortalLab, a Web Services oriented toolkit for designing, integrating and building Semantic Grid portals. Portals built from PortalLab are composed from a collection of reusable Web Services oriented portlets that are themselves semantic Grid services. Each portlet has a WSDL interface and a semantic registry defined in a domain ontology repository. The use of software agents assists end users in formulating domain problems, searching possible solutions (solvers) and submitting user tasks to the Grid. Multiple agents work in a peer-to-peer environment to allow us rs to access federated Grid services across different domains to improve fault toleranc and quality of service in user job submission and execution on th Grid. Since portlets are context independent, a PortalLab portal provides the ability to interoperate with different Grid systems at a portal level.