This publication describes the design of four maintenance tests for the Federal Information Processing Data Encryption Standard (DES).  The tests consist of an iterative procedure that tests the operation of DES devices by using a small program and minimum data.  The tests are designed to be independent of implementation and to be fast enough to test devices during actual operation.  The tests are defined as four specific stopping points in a general testing process and satisfy four testing requirements of increasing degree of completeness depending on the throughness of testing desired.