Cyclic nucleotide-activated protein kinase in locust fat body is elevated by extracts containing adipokinetic hormone (AKH) from locust corpora cardiaca or by synthetic redpigment-concentrating hormone (RPCH) which also exhibits lipid-mobilizing activity. Maximal activation is first attained in vitro 90 sec after RPCH is added to the incubation medium and 3.5 min after addition of AKH extract. This activation reflects the increase in endogenous cyclic nucleotides. Incubation of fat body in the presence of exogenous cyclic nucleotides activates lipase, and RPCH stimulation ultimately elevates the level of transported diacylglycerol 2.3-fold. RPCH stimulates fat body lipase in vivo.