The resistivity at depth of sea ice was measured in McMurdo Sound to give an indirect way of measuring the depth of the percolation layer. This layer is where the sea ice becomes much more permeable to the seawater and hence the conductivity rises significantly. The determination of the depth of the percolation layer is important as it probably controls the behaviour of biological systems in sea ice. Once water movement becomes possible then biological activity is likely to increase. The development of an instrument that will be able to be deployed and left for the period from October until February was tested.