The immunologic patterns of 3 human pituitary adenomas of Cushing’s disease have been studied after gel exclusion chromatography (Sephadex G-50). The immunologic characteristics were examined with three radioimmunoassays specific for human cor-ticotropin (ACTH). lipotropin (LPH) and β-endorphin (β-End). In cell tumor extracts, chromatographic peaks corresponding to β-LPH, γ-LPH, β-End and ACTH were identified. The ACTH/β-LPH-β-End ratio was 1 in the 3 cases. Additionally, in the 3 cases, a chromatographic peak, partially cross-reacting in the β-End assay, was eluted after β-End, thus suggesting the presence of a fragment of the molecule. In 1 case, a peak of large molecular weight material with N- and C-terminal β-LPH and ACTH immunoreactivity was observed, which corresponded to the precursor material.The release and the effects of various stimuli were studied on dispersed tumor cells in primary culture. The tumor cells had a biphasic basal secretion rate with a rapid increase of ACTH/β-LPH-β-End in the culture medium during the first 2 h. Then the release, studied during 2 days, was slower. Chromatographic studies showed that the β-LPH/β-End ratio was 0.8 in the cells and 0.3 in the medium, due essentially to the release of β-End and β-End-like materials. The cells released ACTH and β-LPH-β-End in equimolar ratio after stimulation with arginine vasopressin (AVP). The maximum effect was obtained with 10-6 M AVP (D50 = 1 10-9 M). Dibutyryl cyclic AMP (2 · 10-3 M) induced maximal release of ACTH/β-LPH-β-End. This stimulation was suppressed by a 48-hour preincubation with dexamethasone (10-8–10-6M). There was no effect of TRH and LH-RH on cell release. Dopamine (10-6M) specifically blocked the release of ACTH/β-LPH-β-End in 1 case. These data showed (a) heterogeneity of chromatographic profiles from case to case; (b) the presence of material in the tumor, cell extracts and culture medium corresponding to fragment(s) of β-End; (c) culture studies demonstrated that tumor cells remain responsive to AVP stimulation and dexamethasone suppression, and (d) the dopamine inhibition of ACTH and β-End release needs further investigation.