If viable fibroblasts are used as an active ingredient of an embolic material, it is expected that proliferation and extracellular matrix production of fibroblasts incorporated at a vascular lesion will help restore tissues due to endovascular scar formation, resulting in progressive and permanent occlusion. Based on this working principle, we have devised a novel biological embolic material, hybrid fibroblast incorporated collagen (hybrid FC) beads composed of collagen microbeads and autologous fibroblasts harvested from the subcutaneous tissue of the host to be treated. Hybrid FC beads were prepared by culture of fibroblasts harvested from canine subcutaneous tissue on collagen microbeads (diameters ranging from around 100 µm to around 400 µm). Canine kidneys were embolized with either hybrid FC or cell-free collagen beads via a transarterial route. Histological examination up to 6 months after embolization revealed that, although both embolic materials effectively occluded the target vessels at the time of embolization, intravascular scar formation activity at the embolized sites was much more profound in the case of the hybrid FC beads than in that of the cell-free beads. Proliferation of autologous fibroblasts was verified by the expression of alkaline phosphatase activity of gene-transfected fibroblasts at the site of lodgement of the beads. It is expected that, using the novel hybrid biological embolic material, hybrid FC beads used for vascular lesions such as arteriovenous malformations can be treated more effectively to restore tissues, resulting in minimal recanalization which often occurs when synthetic embolic materials are used. Copyright 1999 Harcourt Publishers Ltd.