It is now over 20 years since dendritic cells (DC) were first identified in and isolated from the spleens of mice (1 ,2 ) and they continue to be a much-studied population. Only a small proportion of spleen cells are DC, but the large size of the organ means that useful numbers of DC can still be purified. In recent years the ability to grow cells with the phenotypic and functional properties of DC from bone marrow progenitors has opened new avenues of research. However, the relationship of cells grown in this way to DC populations in vivo is unknown and the need remains to study DC present in tissues.