The haematology of the Australian sea lion Neophoca cinerea was studied in a breeding colony on Kangaroo Island, South Australia. The methods used to catch and restrain the animals are described and the haematology of 38 animals of varying age and sex groups is recorded. Total values for both erythrocytes and leucocytes were similar to those of other marine mammals and were in the ranges of 4.77 to 6.08 × 10⁶ mm³ and 6.3 to 14.6 × 10³ mm³, respectively. Erythrocytes volumes were very large, measuring from 96 to 112 mm.³ The packed cell volumes ranged from 48.3 to 64.2% and the haemoglobin values from 16.2 to 21 gm percent. The neutrophil lymphocyte ratio varied from 0.5 to 6.2 and in some animals absolute lymphocyte values were less than 1,200 mm.³ In many animals the percentage of eosinophils was greater than 20%, suggesting parasitic disease.