Retinoic acid (RA) and dibutyryl cAMP plus theophilline (CT) trigger F9 cells to differentiate into parietal endoderm, The differentiation induces a 9-fold increase in total heparan sulfate (HStotal) biosynthesis and a 170-fold increase in anticoagulantly active HS (HSact) biosynthesis, Measurement of 3-O-sulfotransferase-1 mRNA and enzymatic activity demonstrated an increase of over 100-fold whereas determination of N-, 2-O, and 6-O-sulfotransferase enzymatic activities showed elevations of 2-, 3.5-, and 3.7-fold, respectively. HSact precursor pool measurements reveal that 30% of control F9 HStotal can be converted into HSact while only an additional 10% of RACT F9 HStotal can be transformed into HSact. Disaccharide analysis of metabolic labeled HS indicated that 32% 3-O-sulfate containing disaccharides, i.e. GlcA-anMan(R)3S and GlcA-anMan(R)3S6S, are present in HSact and 68% GlcA-anMan(R)3S and GlcA-anMan(R)3S6S are found in anticoagulantly inactive HS (HSinact). By using adenosine S'-phosphate 5'-phosphosulfate and purified 3-O-sulfotransferase-1, 30% of 3-O-sulfation occurs in HSact and 70% of 3-O-sulfation occurs in HSinact. The similar ratio of 3-O-sulfate distribution in HSact versus HSinact suggests that HSact production in the F9 system is determined by the abundance of 3-O-sulfotransferase-1 as well as the size of the HSact precursor pool. Extensively 3-O-sulfated HSinact may play an important functional role under in vivo conditions within the murine placenta.