Ubiquitous and pervasive applications are aware of the context of the used resources. This class of application can benefit from mechanisms to discover resources (devices and sensors) that meet their requirements and mechanisms to monitor the state and provide access to the functionalities of these resources. We present an architecture that includes two essential services to compose the supporting infrastructure required by the mentioned applications: a Context Service, that provides access to context information, and a Discovery Service. Resource Agents, which encapsulate and provide access to the actual resources and sensors, are also included in the proposal. A reference implementation, based on Web Services technology, was used to develop a remote assisted living application, which relies on ambient sensors, placed in each room, to capture context information and on a combo medical appliance to perform blood pressure measurements on the patient, according to a care plan prescribed by a doctor. The collected set of context data may be transmitted to a monitoring center and also interpreted locally using medical knowledge; the identification of a patient's abnormal condition can activate local actions or send an emergency message to a monitoring center. The local infrastructure can help a doctor to monitor and assist the patient while he or she is performing daily activities. It may also help reducing hospitalization time and improving the patient’s treatment compliance and quality of life.