The high cost of military vehicle maintenance has led to increased interest in diagnostic aids and procedures. Health screening can provide the basis for reducing scheduled maintenance, by detecting the sequence of events leading to failure at an early stage. The Army is currently developing a testing unit, STE-ICE, that provides testing logic but not diagnostic interpretation. Another approach is miniaturization of equipment so that on-board test devices could be connected or built into the vehicle. DARPA plans a demonstration of such an on-board system, the Vehicle Monitoring System (VMS), to be field tested in 1979. The results will lead to improvements in vehicle design and cost-effective maintenance procedures. The VMS concept is a step toward some future system of built-in diagnostics. Reasons why such systems may develop in the future: emission and fuel consumption regulations may require inexpensive sensors and on-board microcomputers. Thus the addition of a diagnostic function will be attractive.