Regulation of the expression of procholecystokinin (proCCK) and proenkephalin A mRNA was studied in the human neuroblastoma cell line SK-N-MC. Cells were treated with dibutyryl-3',5'-cyclic AMP (dbcAMP), noradrenaline or isoproterenol, a beta-adrenoceptor agonist. Levels of proCCK and proenkephalin A mRNA were determined by Northern blot analysis with proCCK- and proenkephalin A-specific cRNA hybridization probes 9 h after drug treatments. ProCCK and proenkephalin A mRNA were co-expressed in SK-N-MC cells. ProCCK mRNA levels were increased 1.5-2.5 times by dbcAMP, noradrenaline and isoproterenol when compared with controls. The level of proenkephalin A mRNA increased approximately two to three times under the same drug conditions, whereas the level of N-myc mRNA did not change significantly. These results suggest that expression of proCCK and proenkephalin A mRNA may be regulated by a similar cAMP-dependent mechanism in the SK-N-MC cell line.