Experiments were performed to characterize the protein kinase activity in blood lymphocytes from patients with chronic lymphocytic leukemia (CLL). Using histone as a substrate, the average specific activity was 397 pmole/min/mg protein. The Km for ATP was 8 muM and for histone 0.3 mg/ml. The addition of optimal concentrations of cyclic adenosine monophosphate (cAMP) (1 muM) or cyclic guanosine monophosphate (cGMP) (10muM) resulted in a 2.2-fold stimulation in activity but had no effect on the Km for ATP or histone. Most of the properties of the CCL protein kinase were similar to those of the normal lymphocyte enzyme. These include the pH response, substrate affinity, as well as rates of phosphorylation and dephosphorylation. The phosphorylation pattern of endogenous proteins was determined using intact lymphocytes incubated with 32P and cell-free homogenates with AT32P. These results indicate that: (1) the cyclicnucleotide-protein kinase interactions are unimpaired in CLL lymphocytes; and (2) a sharply defined cyclic nucleotide concentration response occurs for CLL (as well as normal) lymphocytes, which may explain the reports of variable inhibitory (and stimulatory) effects on mitogenesis by these agents.