A series of totally implantable telemetry systems has been developed to determine such key physiological parameters as blood flow, pressure, dimensions, temperature, and bioelectrical activity in chronic research animals. Custom integrated circuits provide the signal-processing complexity and performance required to sufficiently instrument the animals for an accurate prediction of human responses. Additional implant and transducer technologies are necessary to complete the instrument package. Although the costs of these technologies are high, they are more than offset by the unique information obtained and overall reduction in the expenses of medical research because fewer animals can be studied over longer periods. A number of the IC-based implants are in use in several physiology and experimental drug studies where adequate reliability and performance could not be achieved by alternate approaches.