6-[Bis-(2-chloroethyl)-amino]-6-deoxy-D-glucose (C-6) is a new glucose-containing nitrogen mustard that has significant activity for murine P388 leukemia with relative sparing of bone marrow in mice. The in vitro myelotoxicity of C-6 compared with that of melphalan, a clinically active, myelosuppressive nitrogen mustard, was determined in the CFU-C assay in human bone marrow samples obtained from normal volunteers. There was no significant difference between the myelosuppressive actions of C-6 and melphalan at any of the concentrations used except for 4.0 microM, at which C-6 was significantly (P less than 0.05) more toxic than melphalan. Both agents decreased the number of bone marrow cell colonies to approximately 12% of control at 6.6 microM (1 h incubation), which is a good approximation of melphalan's CxT (concentration by time) in man. We used the human tumor stem cell assay (HTSCA) to investigate in vitro antitumor activity. We obtained two specimens of malignant melanoma and two of malignant ovarian carcinoma from patients not previously treated with chemotherapy. The antitumor activity of melphalan was either similar to or greater than that of C-6 at all concentrations utilized against any of the four tumor specimens, except at 1.3 microM for tumor I. In particular, there was no significant difference in the antitumor activities of the two agents at 6.6 microM. These results suggest that C-6 will not be less myelosuppressive than melphalan at doses that produce equivalent antitumor activity in man. In addition, C-6 did not demonstrate increased myelotoxicity for normal human bone marrow cells incubated in glucose-deficient medium as against medium containing 300 mg% glucose at any of the concentrations used. This suggests that C-6 is not transported into normal human bone marrow cells via the glucose transport system, despite the presence of a glucose moiety within the molecule.