The complement system helps the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the innate immune system that is not adaptable and does not change over the course of an individual’s lifetime. However, it can be recruited and brought into action by the adaptive immune system. The complement system is also used in research laboratories for in vitro assays during vaccine development, cytotoxicity testings… But how to select to most appropriate Rabbit or Guinea pig complement according to research applications and sample types?