The in vivo host range of human T-cell leukemia virus type 1 (HTLV-1) has not been definitively established. To determine if hematopoietic stem cells from patients with adult T-cell leukemia-lymphoma (ATL) are infected with HTLV-1, we used a clonogenic progenitor assay followed by the polymerase chain reaction for the detection of HTLV-1 DNA. In vitro growth characteristics of myeloid (CFU-GM) and erythroid (BFU-E) progenitor cells among nonadherent T-cell-depleted bone marrow (BM) mononuclear cells (NA-T-MNCs) from 10 patients with ATL was not significantly different from those of HTLV-1-seronegative controls (P = .20); numbers of colonies per 1 x 10(5) NA-T-MNCs were 34.9 +/- 7.6 for CFU-GM and 39.0 +/- 12.5 for BFU-E in patients with ATL, whereas those were 32.1 +/- 9.5 for CFU-GM and 41.4 +/- 12.7 for BFU-E in normal controls. HTLV-1 DNA was not detected in individual colonies formed by CD34+ cells from any of the patients. Similarly HTLV-1 DNA was not detected in 1 x 10(3) CD34+ cells sorted on a fluorescence-activated cell sorter (FACS) from six patients with ATL studied. In contrast, HTLV-1 DNA was detected in BM mononuclear cells from all patients. These observations clearly indicate that hematopoietic progenitor cells from patients with ATL are normal in their colony-forming capacity and that CD34+ cells from patients with ATL are not infected with HTLV-1 in vivo.