Human lymphocyte-associated cell surface protein LAM-1, which includes domains homologous with binding domains of animal lectins, growth factors, and C3/C4 binding proteins, and the cDNA encoding LAM-1, are described. Antagonists to LAM-1 are used in a method of treating a human patient suffering from a lymphocyte-mobilizing condition which involves administering a therapeutic amount of the antagonist in a non-toxic pharmaceutical carrier substance. Additionally, antibodies that bind human LAM-1 and inhibit cellular adhesion, migration or infiltration into tissues are described.