Parallel cultures of adult rat vibrissa dermal papilla cells and skin fibroblasts revealed differences between the two cell types with respect to a number of criteria. In particular the dermal papilla cells demonstrated a distinctive single cell morphology, and at confluence formed cell aggregates radically different from regular fibroblast multilayering and patterning. This finding confirmed repeated observations of papilla cell clumping in short-term culture. The dermal papilla cells which are mitotically quiescent in situ were also shown to have a lower proliferative capacity than the skin fibroblasts. The affinity shown by papilla cells towards each other in culture reflected the behaviour demonstrated by isolated dermal papillae transplanted into ear dermis and into the collagenous capsule of the vibrissa follicle. In the absence of epidermal contact the papilla cells remained as recognizable rounded aggregates for the experimental period of up to nine months. Synthesis of extracellular material typical of that seen in situ was observed, particularly during the first weeks following transplantation. The collective behaviour of the dermal papilla cells revealed in this study may be significant for the morphogenetic activity of the papilla, and for papilla size during the hair cycle. It may also reflect the retention of embryonic-like properties by the dermal component of adult hair follicles.