The redox potentials of lake water have been the subject of several investigations (Kusnetzow 1935, Pearsall & Mortimer 1939, Hutchinson, Deevey & Wollack 1939, Deevey 1941, Allgeier, Hafford & Juday 1941, Mortimer 1941-42). The ecological significance of the redox potentials is stressed in several of these works. The work of Mortimer (1941-42) also shows the importance of the seasonal variations in redox potentials for the liberation from the sediments of different important nutrients.

At present very little is known about the redox potential of the deep water in meromictic lakes. Allgeier, Hafford & Juday (1941) recorded vertical distribution of redox potential in one meromictic lake, Lake Mary, Wisconsin. The redox potential of the monimolimnion of Lake Mary varied from Eh = 0.140 volts at 8 m to Eh = 0.075 volts at 20.5 m. Hutchinson (1957) assumes it probable that other, but by no means all, meromictic lakes will be found to show a similar phenomenon.

In the present paper the vertical distribution of redox potential of the water of three meromictic and one oligomictic lake is described.