This paper continues the discussion of an immersion method of refractometry of living cells, the basic principles of which were given in Part I (Barer and Joseph, 1954). A suitable immersion medium should be non-toxic, must not penetrate the cell, and must be in osmotic equilibrium with it so that no change in volume (and hence in concentration) occurs. These requirements are best met by solutions of substances of higTf molecular weight. The effects observed when cells become freely permeable to such substances are described. An account of tests with various immersion media is given. The main substances tried have been peptone, proteose, protein hydrolysate, dextran, polyvinyl alcohol, polyvinylpyrrolidone, acacia gum, egg albumin, bovine gamma globulins, carboxyhaemoglobin, and bovine plasma albumin. Of these, bovine plasma albumin has proved to be most generally useful though acacia gum may be a good inexpensive substitute for some cells, particularly fungi.