We observed the apparent migration of Langerhans cells across the basal lamina of normal human skin by immunoelectron microscopy using monoclonal anti-T6 antibody. This technique made it possible to visualize cytoplasmic processes of Langerhans cells not normally detectable by routine transmission electron microscopy, and therefore facilitated the documentation of the migratory process. Although events early in the migratory sequence were not observed, perhaps as the result of the evanescent nature of this phase, the association of Langerhans cells with focal disruptions in the epidermal basal lamina was documented. The basal lamina adjacent to these Langerhans cells was electron lucent, granular in character, and thinned, or intact, suggesting sequential reassembly after disruption. This study provides ultrastructural documentation supporting the hypothesis of ongoing migration of Langerhans cells across epidermal membranes, and suggests that this process is mediated by the disruption and reconstitution of the epidermal basal lamina.