Dendritic cells (DC) from human peripheral blood were enriched using a method including adherence on plastic, depletion of phagocytic cells, flotation on density gradient column and panning on antibody-coated surfaces. The course of cell separation was evaluated by characterizing the morphological, antigenic and functional features of the different cell fractions. Using the population depleted of strongly adherent cells as the source, we were able to achieve a cell fraction containing 40-65% of DC (the main contaminants being monocytes and natural killer cells). Functionally these cells were highly stimulatory in autologous mixed leukocyte reaction. On the other hand, cells which primarily adhered well and were detached after overnight culture contained less than 5% of DC (the main contaminants being monocytes) after the same purification protocol. The calculated yields of DC were 1-2 X 10(6) and less than 0.5 X 10(6) from the nonadherent and adherent populations, respectively. Thus we concluded that the adhesiveness of DC from human blood is so weak that they can more efficiently and in a more reproducible way be enriched from the primarily nonadherent cell fraction.