Performance of delivery systems for delivering beneficial agents to an animal are monitored to determine the delivery rate of the beneficial agent and the proper operation of the beneficial agent delivery device. Performance monitoring can be achieved by monitoring the physical configuration of the implanted osmotic delivery device from the exterior of the body to determine the amount of beneficial agent delivered and/or the delivery rate of the beneficial agent. The monitoring of the physical configuration of the implanted osmotic delivery device may be performed in different manners such as by X-ray or fluoroscopic monitoring of the implant structure or magnetic determination of a piston location within the implant. Performance monitoring can also be achieved by use of a performance marker within the beneficial agent to produce a specifically detectable response which can be measured noninvasively in body fluids or by-products.