Twelve male weight lifters were used to study the effect of oral arginine consumption on growth hormone (hGH) , arginine (Arg), and somatomedin (IGF-1) concentrations. Subjects were randomly assigned to treatment or placebo groups. Following a week of controlled exercise and diet, fasted subjects took either an acute dose of arginine hydrochloride or casein (placebo), at 0.1 g/kg BW. Blood samples were drawn every 15 min, for 90 min after ingestion. All samples were analyzed for hGH and Arg, and IGF-1 was measured in the baseline sample. Subjects then underwent 10 days of caloric restriction, consuming a liquid diet of 22 kcal/kg BW/d. Subjects took either arginine or casein supplements in two doses of 0.1 g/kg BW twice daily, for a total dose of 0.2 g/kg BW/d. The weight lifting protocol remained unchanged. On day 17, subjects were again tested for the acute response to a single dose of 0.1 g/kg BW supplement (arginine or placebo) over 90 min. Blood was collected and analyzed as before. No change in hGH and Arg occurred 90 min after consumption of the arginine supplement, regardless of dietary condition. However, arginine supplementation caused overall higher hGH and Arg levels (2.64 ng/ml and 0.87 mmol/l) compared to placebo (1.36 ng/ml and 0.71 mmol/l) during caloric restriction. IGF-1 did not change in either group under either diet. Thus, oral arginine supplementation at 0.1 g/kg BW did not produce a rise in hGH or Arg after 90 min, and did not affect overall hGH status, as measured by IGF-1, during energy restriction and supplementation. / Master of Science