A static cold vapour procedure for the determination of mercury by atomic-absorption spectrometry using a very simple and inexpensive apparatus is described. The mercury-laden air is forced into the absorption cell by water displacement. Maximum sensitivity is obtained when the volume of the displaced air is equal to the internal volume of the absorption cell, and the mercury solution is 9 M in sulphuric acid. The peak absorbance exhibited a marked decline for hydrochloric acid concentrations above 1.5 M and for nitric acid concentrations above 3 M. The calibration graph obtained for mercury(II) in 9 M sulphuric acid is linear from 0 to 17 ng ml^–1, and the sensitivity is 0.08 ng ml^–1. A windowless absorption cell can also be used with a narrower linear calibration range. The detection limit was found to be 0.08 ng ml^–1 for both cells with and without end windows.