This study aimed to investigate the possible changes in serum leptin concentration caused by acute exercise and the effects of zinc deficiency on these changes. Forty male rats were divided into control-control, control-exercise, zinc-deficient-control, and zinc-deficient-exercise groups (10 rats in each). Control-exercise and zinc-deficient-exercise groups performed exercise at 6 m/min speed on a rodent treadmill for 60 min or until exhaustion. All rats were decapitated 48 h after the exercise, and blood samples were collected to determine serum leptin and zinc levels. Serum leptin levels in the exercise groups were lower than in the control groups. Leptin levels in the zinc-deficient-control group were lower than in the control-control group. The mean exercise time of control-exercise group was significantly longer than the zinc-deficient-exercise group. We conclude that serum leptin levels significantly decrease both 48 h after strenuous exercise and in the zinc-deficient rats, and there is a further decrease in leptin levels when rats fed on a zinc-deficient diet performed exercise. © Copyright 2005 by Humana Press Inc. All rights of any nature, whatsoever, reserved.