The wavelength shifts for the green (5460A) and blue (4358A) lines emitted from an electrodeless discharge lamp of Hg 198 have been studied as a function of the temperature of the water jacket of the source. The values of the wavelength shifts observed for the green and the blue lines are (8.5±3) 10 -6 A/°C and (2±1) 10 -6 A/°C, respectively.