Human papovavirus JC, previously passaged in amnion cells or in primary human fetal glial cells, replicated efficiently in urine-derived epithelial cells. Primary isolation of the virus from brain extracts was possible in urine-derived cells, but these cells were not as sensitive as primary human fetal glial cells for this purpose. Primary isolations of human papovavirus JC from urine sediments of renal transplant patients were made in urine-derived cells.