Sarcolectin was originally described as an interferon antagonist, first detected in normal human muscles and in osteosarcomas. On the basis of a functional analysis of the protein, we postulated that the interferon antagonist is in fact an animal lectin . When cloned and expressed, the recombinant protein was found to be of 55 000 M . Fragments of sarcolectin molecules, when bound to albumin, react together in immune assays and create a 65 000-55 000 M complex and cannot be removed by heat denaturing or standard sodium dodecylsulphate gel-electrophoresis techniques. The biological functions of these sarcolectin proteins (from apparently various cellular origins) can be summarized as follows: (i) they promote agglutination of normal or malignant cells, because of their affinity for cell membrane bound sugars; and (ii) they inhibit the synthesis of the secondary proteins responsible for all the interferon-dependent biological functions that lead to the antiviral state. Consequently, the original virus-sensitive state is restored in the cells . Furthermore, in such sarcolectin-treated cells, refractoriness to a second interferon induction is diminished or abolished . They stimulate cellular DNA synthesis in all immune-competent cells, as well as in epithelial cells and fibroblasts in conformity with the known general properties of lectins. [1,2] r r [3]