Abstract: Disclosed is a mercury electrodeless discharge lamp for use in spectrophotometric analysis, particularly atomic absorption spectrophotometry, and a method of its fabrication. Unreduced mercuric oxide (HgO) is employed as the source of mercury in the lamp. In fabricating the lamp, a small quantity of mercuric oxide is introduced into a lamp bulb which has been previously cleansed and flushed with noble gas. The bulb is heated to a temperature just below the decomposition point of the mercuric oxide. The bulb is then flushed with a noble gas, filled to the desired pressure with a noble gas and sealed.