Background: Amino acids have been reported to act as modulators of various regulatory processes and to provide new therapeutic applications for either the prevention or treatment of metabolic disorders. The purpose of the present study is to investigate the effects of single oral dose administration and a continuous treatment of L-tryptophan (L-Trp) on the regulation of blood pressure and glucose metabolism in stroke-prone spontaneously hypertensive rats (SHRSP). Methods. First, male 9-week-old SHRSP were administered 100 mg L-Trpkg -1 body weight in saline to the L-Trp group and 0.9% saline to the control group via a gastric tube as a single oral dose of L-Trp. Second, three groups of SHRSP were fed an AIN-93M-based diet supplemented with L-tryptophan (L-Trp) (0, 200, or 1000 mgkg-1 diet) for 3 weeks as continuous treatment of L-Trp. Results: Single oral dose administration of L-Trp improved blood pressure, blood glucose, and insulin levels. Blood pressure, blood glucose, and insulin levels improved significantly in the L-Trp treatment groups. The administration of L-Trp also significantly increased plasma nitric oxide and serotonin levels. Conclusion: L-Trp by both single oral dose administration and continuous treatment improves glucose metabolism and blood pressure in SHRSP.