C5-deficient serum was supplemented with 33% serum from CLL or NC or with purified C5 (positive control, PC). C activity was assessed by sC5b-9 levels before and after activation with aggregated IgG via the CP (A) or with Zymosan via the AP (B). The increase (delta) in sC5b-9 levels above baseline is presented (mean with SD). C5-deficient serum before supplementation (squares, n = 3) and in C5-deficient serum supplemented with normal C5 as positive control (PC, Diagonals, n = 3), NC sera (white bars, n = 7), sera from CLL patients with normal C5 (grey bars, n = 6) or sera from CLL patients with abnormal C5 (black bars, n = 7). *p<0.01 vs. all, except for the group of CLL patients with normal C5. **p<0.01 vs. all.