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The disposition of growth hormone releasing peptide (SK&F 110679) has been studied in male Sprague-Dawley rats and in male and female beagle dogs following intravenous (iv) and subcutaneous (sc) administration. Mass balance/excretion of [3H]SK&F 110679 was assessed in bile duct-exteriorized rats from which radiolabeled biliary and urinary excreta were quantified and characterized. [3H]SK&F 110679 was excreted, predominantly in the bile, and to a large extent as intact peptide following either iv or sc administration. Although the extent of biliary excretion of radiolabel was similar following iv or sc administration (60-70% of the dose), the rate was significantly higher following iv administration. Using a specific plasma HPLC/fluorescence assay, the iv and sc pharmacokinetics of SK&F 110679 were investigated in both species. Following iv bolus administration, biphasic plasma concentration-time profiles were observed, and the initial phases were characterized by 2-4 min half-lives. Systemic plasma clearance was 27 ml/min/kg in the rat (0.4 mg/kg dose) and 17 ml/min/kg in the dog (0.5 mg/kg dose). High sc bioavailability (89-103%) was observed in both species; an apparent terminal half-life of 1 hr likely reflected slow absorption from the injection site.