Description: Transfusion therapy is the mainstay of supportive treatment for dogs and cats with anaemia. The commercial availability of blood and blood products for dogs has resulted in an increase in the number of patients benefiting from transfusion therapies. This article, the first of two discussing the use of blood transfusions in dogs and cats, outlines the indications for transfusion therapy and describes the different options available. Part 2, to be published in the June issue of In Practice, will discuss the practicalities of blood collection in situations where blood products are either unavailable or inappropriate, and will describe how to administer transfusions safely.