WinRho® SDF is licensed in the USA, Canada and Europe to treat ITP and prevent Rh isoimmunization. Although safe, efficacious and cost-effective, WinRho® SDF has only been available in a freeze-dried formulation. In order to simplify injection preparation and reduce the possibility of preparation errors, a liquid formulation of WinRho® SDF has been developed. The pharmacokinetics and tolerability of the liquid and freeze-dried preparations were compared in 2 randomized, double-blind, multi-center phase 1 studies that were conducted in healthy adult volunteers. Subjects were administered one of the formulations either IM (300 μg or 15 μg/kg) or IV (50 μg/kg). Pharmacokinetics (AUC, Cmax, t1/2, tmax) and safety data (adverse events and laboratory assessments) were assessed over 84 days. In total, 142 subjects received either the liquid or freeze-dried formulations (N=71 each group). Following IV or IM administration, the ratios (90% confidence intervals) for AUC and Cmax were within the FDA required acceptance range of 80–125% to demonstrate bioequivalence. Both formulations had comparable half-lifes of ~18–19 days and ~26 days following IV or IM administration, respectively. While tmax occurred immediately following IV administration, tmax was ~3–7 days after IM administration. Both formulations were similarly tolerated following either IV or IM administration. The most common adverse events were headaches and neck/back pain. Liquid WinRho® SDF was demonstrated to be bioequivalent to the freeze-dried formulation following IV or IM administration. This suggests that liquid WinRho® SDF may be therapeutically equivalent to the freeze-dried formulation and provide a more convenient presentation for use.