Sickle cell adhesion to laminin is inhibited by the 4C7 MoAb. Immobilized laminin was treated with the 4C7 antilaminin MoAb (4C7 MoAb) in ascites before the 1% hematocrit flow adhesion. Concentrations of the 4C7 IgG₂ in ascites ranged from 15.0 to 37.5 μg/well. Adhesion of sickle RBCs to laminin was greatly reduced by the 4C7 MoAb, but not by an isotype-matched IgG₂control antibody at amounts up to 37.5 μg/well or by ascites fluid isolated from the commercial 4C7 preparation. Adhesion to human laminin in the absence of antibody is presented as a negative control. Data shown represent 10 experiments involving 4 patients.