We describe the dynamics of three-dimensional fluid vesicles in steady shea
r flow in the vicinity of a wall. This is analyzed numerically at low Reyno
lds numbers using a boundary element method. The area-incompressible vesicl
e exhibits bending elasticity. Forces due to adhesion or gravity oppose the
hydrodynamic lift force driving the vesicle away from a wall. We investiga
te three cases. First, a neutrally buoyant vesicle is placed in the vicinit
y of a wall that acts only as a geometrical constraint. We find that the li
ft velocity is linearly proportional to shear rate and decreases with incre
asing distance between the vesicle and the wall. Second. with a vesicle fil
led with a denser fluid, we find a stationary hovering state. We present an
estimate of the viscous lift force that seems to agree with recent experim
ents of Lorz et al. [Europhys. Lett. 51. 468 (2000)]. Third, if the wall ex
erts an additional adhesive force, we investigate the dynamical unbinding t
ransition that occurs at an adhesion strength linearly proportional to the
shear rate.