Large quantities of cultured human facial dermal fibroblasts were propagated from randomly selected patients to determine their relative suitability as percutaneously injectable living implants. Volumetric and histologic comparisons were made between the following implants that were injected subcutaneously into athymic nude mice: (1) cultured human fibroblasts (HFb); (2) cultured human fibroblasts dispersed in Zyderm II collagen (HFb + Zyd); (3) Zyderm II collagen (Zyd); and (4) Zyplast collagen (Zyp). Both the HFb and HFb + Zyd implants were accepted as primary takes but regressed volumetrically at significantly greater rates than either the Zyd or Zyp implants. Correlative immunohistochemical staining revealed that, by 10 days, 90% of the cells within the HFb implants and 80% within the HFb + Zyd implants were of human origin; however, by 9 weeks, approximately 25% of the cells were of human origin in both types of implants. These results indicated that cultured human fibroblasts can be successfully injected as living grafts; however, the subsequent gradual attrition in the numbers of implanted cells, as noted in this model system, limits the long-term retention of the implants.