A description is given of a high- resolution spectrometer which uses a dye laser, stabilized relative to a reference cavity by means of a multistage system with two He-Ne lasers, one free- running and the other Lamb- dip- stabilized. This spectrometer was used to measure the isotopic shifts of the naturally occurring isotopes of krypton and of radioactive **8**5Kr and **2**2Na (relative to **2**3Na).