2C11-1-5 recognizes human IgM, baboon IgM and IgM from the following monkeys: Rhesus, Cynomolgus, African Green and Squirrel. It does not recognize Capuchin monkey IgM. Other species have not been tested. No reactivity is observed with monkey IgG or IgA. Human IgM can be used as standard in immunoassays for IgM from all reactive species listed above.