The population structure of Euphausia crystallorophias (krill) was investigated as part of a study of the under ice pelagic ecosystem in McMurdo Sound. On six occasions vertical hauls were made from the surfaace to 500m depth using a 1mm mesh free fall plankton net. The E. crystallorophias were removed from the fresh samples and the sex was determined of the mature and where possible, the immature animals. The length of each animal was measured ot the nearest millimeter and wet weights were measured. The distribution of E. crystallorophias in the water column was determined from zooplankton hauls taken at the six depths of 0, 25, 75, 150, 275 and 500m.