Peanut agglutinin (PNA) is plant lectin protein derived from the fruits of Arachis hypogaea. Peanut agglutinin may also be referred to as Arachis hypogaea lectin. 

The lectin has a molecular weight of 110 kDa and consists of four identical subunits of approximately 27 kDa each. PNA does not agglutinate normal human erythrocytes, but strongly agglutinates neuraminidase treated erythrocytes. Lectin PNA is specific for terminal β-galactose and binds preferentially to a commonly occurring structure, galactosyl (β-1,3) N-acetylgalactosamine. PNA has potent anti-T activity similar to the anti-T antibody in human sera. PNA has been used in tumour tissue determination for transitional mucosa malignancies. 

PNA is useful in distinguishing between normal and tumor tissues and in assessing malignancy in transitional mucosa. In addition, PNA binding can be used to measure cellular maturity in lymphoid tissues, to distinguish a variety of lymphocyte subpopulations in man and experimental animals, and to measure the levels of lymphoid cell populations in many diseases. PNA can be employed in the fractionation of stem cells in mice for use in bone marrow transplantation across histocompatibility barriers.