Seeds of Artocarpus integrifolia (jack fruit) contain large amounts of the anti-T lectin, jacalin. The mature seeds of jack fruit were homogenized in 0.25 M sucrose and separated by differential centrifugation into four fractions, viz wall, intermediate, and microsomal pellets and soluble supernatant. The lectin activity was associated with the wall pellet collected at low speed centrifugation. The other three fractions obtained by centrifugation at gradually higher speeds contained a similar lectin but of very low specific activity. The distribution pattern of jacalin remained unchanged in the presence of EDTA and/or Triton X-100 indicating that the lectin was not membrane bound. Immunofluorescent staining of jack fruit seeds showed that jacalin was localized in the cell wall in the intracellular space, which corroborated the results of fractionation studies. The possible relevance of these results to the function of lectin in the plant cell is discussed.