Tryptic digestion followed by radioimmunoassay for (Leu)enkephalin-Arg6 has been used in this study as a general method to detect the presence of all possible products containing the enkephalin sequence from the opioid peptide prohormone, proenkephalin B. Tissue extracts of human hypothalamus and pituitary were examined. Gel filtration was used to separate the different precursor products according to molecular weight. The elution profile was also monitored with highly sensitive radioimmunoassays for dynorphin A and dynorphin B, respectively. Immunoreactive dynorphin A appeared in three peaks with the approximate molecular weight of 1000, 2000 and 5000. Immunoreactive dynorphin B partly occurred in other peaks, 1500, 5000 and 10 000 dalton. Profiles obtained by measuring immunoreactive (Leu)enkephalin-Arg6 in all fractions from gel filtration after trypsin digestion showed a more complex pattern compared to the profiles of immunoreactive dynorphin A and dynorphin B. The major peaks coincided with dynorphin A and dynorphin B but high levels of immunoreactive (Leu)enkephalin-Arg6 were also generated from higher molecular weight regions (MW greater than 5000).