AbstractHeparan sulfate from the surface of a variety of mouse cells at different cell densities was examined by ion‐exchange chromatography. The results of this analysis show that:1The heparan sulfate from new isolates of Swiss 3T3 cells transformed SV40 virus (a DNA tumor virus) elutes from DEAE‐cellulose at a lower ionic strength than that from the parent cell type. This finding confirms our earlier observation with an established SV40‐transformed cell line (Underhill and Keller, 1975) and eliminates the possibility that this change is caused by extended passage in culture.2For both parent and transformed 3T3 cells, the heparan sulfates from low and high density cultures were the same as judged by chromatography on DEAE‐cellulose. This result demonstrates that the transformation‐dependent change which we have observed is independent of cell density.3The heparan sulfate from Balb/c 3T3 cells transformed with Kirsten murine sarcoma virus (an RNA tumor virus) elutes from DEAE‐cellulose prior to that from parent Balb/c 3T3 cells. This result extends the transformation dependent change in heparan sulfate to the Balb/c 3T3 cell line and to cells transformed with a