We describe specific two-site immunochemiluminometric assays able to directly measure human growth hormone-releasing hormone 1-44 NH2 and 1-40 OH concentrations in unextracted plasma. A common N-terminal antibody was purified from polyclonal rabbit antisera to growth hormone-releasing hormone 1-44 NH2 on a growth hormone-releasing hormone 1-29 NH2 linked affinity column and labelled with chemiluminescent acridinium ester. C-terminal specific monoclonal antibodies to growth hormone-releasing hormone 1-44 NH2 and 1-40 OH were raised in Balb/C mice and used as solid phase antibodies. Assay of fasting specimens from normal individuals gave medians (and ranges) of 23 pg/ml (2-200) and 30 pg/ml (3-134) for growth hormone-releasing hormone 1-44 NH2 and 1-40 OH, respectively. Samples from a series of acromegalics showed that most have values in the normal range though median values were higher, 56 pg/ml for growth hormone-releasing hormone 1-44 NH2 (P < 0.001) and 52 pg/ml for 1-40 OH (P < 0.001). Using these assays it will be possible for the first time to directly study the physiology and pathophysiology of these two peptides.