Among four different lymphoid populations, sensitivity to rolipram mirrors sensitivity to dbcAMP. One million CLL cells (□), resting (▪) or anti-Ig activated (▧) CD19⁺ cells, or IL-2–supplemented WMC (▧) were cultured for 72 hours with 10 μmol/L rolipram, 40 μmol/L forskolin, or the indicated dbcAMP concentration (in μmol/L) before measurement of apoptosis by Hoechst 33342 flow cytometry. The SEMs of triplicate cultures are indicated.