Variable levels of [Ca2+]i induced in cases of CLL by ligation of sIgM. Lymphocytes from 3 cases of CLL were labeled with the calcium-sensitive dye Fluo-3–AM and analyzed by flow cytometry before and after addition of F(ab′)2 anti-IgM. Density plots illustrate (A) complete response, (B) no response, and (C) partial response. In panel D, responses were quantitated by determining the peak percentage of CLL cells with fluorescence intensity above the unstimulated threshold (T). T was set at the 85th percentile of the fluorescence intensity of unstimulated cells, as shown.