Daratumumab, a human monoclonal antibody targeting CD38, is approved as monotherapy and in combination regimens for patients with multiple myeloma (MM). Currently, daratumumab is administered IV. The phase 1b PAVO (MMY1004) study evaluated subcutaneously administered daratumumab in combination with the recombinant human hyaluronidase PH20 enzyme (rHuPH20) in patients with relapsed or refractory MM. Part 1 of the study, reported here, evaluated a mix-and-deliver (MD) formulation of daratumumab and rHuPH20 (DARA-MD) administered by subcutaneous infusion. Patients received subcutaneous daratumumab according to the approved IV monotherapy dosing schedule at 1200 mg (n 5 8) or 1800 mg (n 5 45). Primary end points were safety and pharmacokinetic (PK) variables. The most common treatment-emergent adverse events with DARA-MD 1200 mg were thrombocytopenia, upper respiratory tract infection, insomnia, and decreased appetite (37.5% each). Anemia (33.3%), upper respiratory tract infection, pyrexia, and diarrhea (26.7% each) were the most common treatment-emergent adverse events with DARA-MD 1800 mg. One patient in the 1200-mg dose group (12.5%) and 11 patients in the 1800-mg dose group (24.4%) experienced infusion-related reactions, which were generally grade 1/2 and typically occurred at the first infusion. The 1800 mg dose achieved similar or greater serum concentrations compared with the 16 mg/kg IV dose. Overall response rates of 25.0% and 42.2% were achieved with 1200-mg and 1800-mg DARA-MD, respectively. Subcutaneous administration of DARA-MD was well tolerated in patients with relapsed or refractory MM, with the 1800-mg dose exhibiting PK concentrations and responses consistent with IV daratumumab in a similar patient population. This study was registered at www.clinicaltrials.gov as #NCT02519452.