The saponification of fish liver oils may increase the activity of the vitamin D. In some cases the increases reached 100 per cent. That the increases were due to different activities of the esterified and free forms of the vitamin was demonstrated by a sample of vitamin D2 palmitate undergoing a 250 per cent increase in activity upon saponification. Halibut liver oils showed anomalous behaviour in this respect, saponification resulting in either increased or unaltered activity, depending on the previous history of the material.