Phytohemagglutinin is a lectin extracted from red kidney beans (Phaseolus vulgaris). The protein consists of two mo- lecular species, a leucoagglutinin (PHA-L) and an erythroagglutinin (PHA-E). Each of the proteins contains a family of five isolectins, each being a tetramer held together by noncovalent forces. PHA-M is the mucoprotein form and is a crude extract used for the stimulation of cell proliferation in lymphocyte culture. PHA-M also has a powerful erythroagglutinating property and it was originally used for separating leukocytes from whole blood.

PHA-M is a sterile, frozen solution of an aqueous extract from selected red kidney beans.