AIM: The aim of our prospective study was to optimize the determination of the pituitary somatostatin receptor status by means of 111-In-pentetreotide scintigraphy and to compare it intraindividually with the pharmacological effect of octreotide in active acromegaly. METHODS: In n = 22 patients with growth hormone (GH) secreting pituitary adenoma, 111-In-pentetreotide scintigraphy was performed, and the specific radionuclide accumulation in the pituitary area (evaluation visually as well as semiquantitatively by means of ROI technique and calculation of various uptake indices) was correlated with the acute drop of GH after administration of 100 micrograms octreotide s. c. (octreotide acute test). RESULTS: The uptake index we propose (cts/pixel-ratio circular pituitary ROI: irregular cerebrum ROI after background correction in the sagittal SPECT slice with maximum pituitary uptake 24 h p.i.) correlates best with the pharmacological effect (acute decrease of GH levels) of octreotide; its upper normal limit amounts of 3.5. CONCLUSION: As often the normal pituitary gland can be visualized scintigraphically, the purely visual differentiation between a normal and a pathological receptor status sometimes is equivocal. A pituitary uptake index, calculated by means of a standardized ROI technique, facilitates this discrimination and so contributes to select possible responders for a treatment with octreotide.