Abstract: A computer controlled system for the diagnostic testing of two wire telephone lines. The system comprises a control means having a programmed digital computer and associated memory, a line test network, a user station and an interface for interconnecting these elements and one or more telephone exchanges and a plurality of two wire telephone lines extending from the exchanges. The line test network is responsive to the digital computer and includes means for generating a plurality of line characteristic signals during a test cycle for a selected line. The characteristic signals are representative of the resistance and reactance between a reference potential and each of the two wires of a selected line, and between the two wires of the selected line. The line characteristic signals are transformed to signals indicative of the line identity, line length, type of termination, type and location of equipment connected to the line and existence, approximate location and type of faults along the line.