The cold adaptation in the proteins/enzymes of Antarctic fish was investigated in collaboration with the American Antarctic program. The likely function of lactate dehydrogenase (LDH), the only isozyme found in these fish, was examined by looking at the amount and distribution of LDH in a variety of both temperate and Antarctic fish. Small samples were collected from 7 different tissues (eye, ... brain, heart, liver, spleen and red and white muscles) of 4-8 individuals of each species of fish (Pagothenia borchgrevinki, Trematomus nicolai, T. newnesi and T. pennelli). Each sample was assayed by creating an extract from a tissue chunk, removing the debris by centrifugation and the produced supernatant assayed for enzyme activity spectrophotometrically. To determine the nature of the new isozyme found in these fish, tissue was collected and stored. A protocol was developed to stabilize the isozyme, to be able to purify it and then determine the amino acid sequence of the amino terminus, in order to identify the new type of isozyme. Lactate dehydrogenase, the enzyme, and another enzyme, citrate synthase, are important in the metabolism of these fish. A survey of the enzyme activity of these enzymes in a number of species of fish was completed. Samples were collected from 7 different tissues from 8 individuals of P. borchgrevinki, T. nicolai, T. newnesi and T. pennelli and analysed for enzyme activity.