Continuous monitoring of software systems under production workload provides valuable data about application runtime behavior and usage. An adaptive monitoring infrastructure allows controlling, for instance, the overhead as well as the granularity and quality of collected data at runtime. Focusing on application-level monitoring, this paper presents the DProf approach which allows changing the instrumentation of software operations in monitored distributed applications at runtime. It simulates the process human testers employ-monitoring only such parts of an application that cause problems. DProf uses performance objectives specified in service level agreements (SLAs), along with call tree information, to detect and localize problems in application performance. As a proof-of-concept, DProf was used for adaptive monitoring of a sample distributed application.