The isotope shift in the spark spectrum of dysprosium was studied by means of a photoelectric recording Fabry-Perot spectrometer with digital data output. For 29 lines the isotope shift of162Dy and164Dy was measured in order to check the mixing of the three configurations 4f 95d6s, 4f 95d 2, and 4f 106p calculated by Wyart. By means of the sharing rule the configuration mixing could be confirmed as a whole. In the ground state configuration the influence of relativistic effects was demonstrated and explained by theory. The order of magnitude of crossed-second-order effects contributing to the isotope shift of 4f 106s6 I and4 I could be estimated. In three lines the isotope shift of all stable Dy isotopes was measured. Mass shift and field shift were separated by comparison with results obtained in the arc spectrum.