Thus, we undertook a study to close mass balance on Heparin sodium injection USP vials manufactured by Baxter Healthcare Inc. Two unopened boxes containing 25 × 1 ml vials (LOT. 117050, EXP. 11/2009) with each vial containing 5000 USP units/ml (Figure 1) were given to our laboratory in early 2008 after they were pulled from the hospital formulary as part of the voluntary recall of suspect lots of HP. These sealed vials were kept under lock and inventory control and provided on a vial-by-vial basis to analysts in our laboratory for the current studies.