Plasma of myeloma patients treated with DARA resulted in agglutination of screening cells (I, II, III). Simultaneous incubation of screening cells with 15 µL DARA-Fab inhibited the agglutination reaction efficiently. In patients 1, 2, and 3, blood was drawn 7, 0, and 2 weeks after the last DARA administration and after 15, 13, and 1 full DARA administrations, respectively.