Background: Efgartigimod, a human immunoglobulin G1 (IgG1) antibody Fc fragment, reduces IgG levels through neonatal Fc receptor blockade. Efgartigimod PH20 SC (1000-mg fixed dose, coformulated with recombinant human hyaluronidase PH20) is provided in a vial administered via a separate syringe (V+S). Here, we investigate bioequivalence, safety, and tolerability of efgartigimod PH20 SC administered via prefilled syringe (PFS) vs V+S in healthy participants. Methods: Bioequivalence was assessed in a phase 1, open-label study. Healthy participants (n=72) were randomized to receive one injection of efgartigimod PH20 SC via PFS or V+S in a crossover design. Separate studies evaluated feasibility of different injection speeds and usability of the PFS. Results: Bioequivalence between efgartigimod PH20 SC via PFS or V+S was established, as the 90% CI around the geometric least-squares mean ratio of Cmax and AUC0-inf was within predefined criteria (80.00%-125.00%). Most adverse events were mild to moderate. No observed differences in incidence of reported injection site reactions emerged. No serious adverse events or deaths occurred. Rapid (20-second) administration was feasible and the PFS could be safely prepared and administered by participants/caregivers. Conclusions: Efgartigimod PH20 SC administered via PFS is bioequivalent to efgartigimod PH20 SC administered via V+S, which may provide an additional convenient treatment option.