Langerhans cells (LC) were enriched from a human epidermal cell (EC) suspension by a rosette-forming technique. First EC were sensitized with the monoclonal antibody OKT6, and then they were mixed with ox erythrocytes (ORBC) coated with affinity-purified rabbit IgG anti-mouse IgG antibodies. Rosette-forming LC were then separated from non-rosetting EC by means of Percoll flotation. After hypotonic lysis of the ORBC, the cells obtained had a viability greater than 90%, and 67-98% of the viable cells were OKT6-positive. In functional studies the enriched cells were strongly stimulatory for allogeneic lymphocytes and were able to function as antigen-presenting cells for the T-cell response to the soluble antigen purified protein derivative.