Symbolic testing and a symbolic evaluation system called DISSECT are described. The principle features of DISSECT are outlined. The results of two classes of experiments in the use of symbolic evaluadon are summarized. Several classes of program errors are defined and the reliability of symbolic testing in finding bugs is related to the classes of errors. The relationship of symbolic evaluation systems like DISSECT to classes of program errors and to other kinds of program testing and program analysis tools is also discussed. Desirable improvements in DISSECT, whose importance was revealed by the experiments, are mentioned.