B19 parvovirus is absolutely tropic for human erythroid progenitor cells. Among the untested mechanisms underlying this tropism is the possibility of cell-specific positive regulation of the promoter in permissive cells. Using the bacterial chloramphenicol acetyltransferase and firefly luciferase reporter genes, we detected strong activity from the B19 P6 promoter in transfected nonpermissive cells. Very high-level expression was seen in a T lymphoblastoid cell line, CEM. No transcriptional enhancement occurred in an erythropoietin-dependent semipermissive cell line. A putative second B19 promoter at map unit 44 (P44) was nonfunctional and unable to confer tissue specificity. Thus, tropism is unlikely to be regulated at the level of transcriptional initiation from either the P6 or P44 promoter.