SYMOP -- an improved computer program for the derivation of symmetry operations from the space-group symbols. The program SYM (1982) for the derivation of the symmetry operations from the space-group symbols is improved. In the new program the symbol is checked for validity. In addition to the symmetry operations a group multiplication table is computed and seminvariance conditions are evaluated. Different settings of the 230 space-group types described by 541 different symbols can be generated using the origins of the International Tables or origins fixed by the user. Computer language is FORTRAN IV.