In this study, we investigated the effects of L-Arginine, which increases the production of nitricoxide (NO) with vasodilative actions, on forearm bathing. The subjects were 12 healthy adult males with 24±1 years old. We compared the changes of blood pressure, heart rate, deep/superficial temperatures, and dermal blood flow by forearm batlmg with or without the oral ingestion of 2000mg L-Arginine. After a 30-minute rest following ingestion, the subjects took a forearm bathing ; immersion of the right forearm below the elbow in 41°C hot water for 15 minutes. There were no significant differences neither in blood pressure, heart rate, nor sublingual temperature between the changes by L-Arginine and water ingestion. Although the superficial temperature of the left toe was significarttly increased 15 minutes after the start of bathing regardless of the presence or absence of L-Arginine (p<0.01), the increase with L-Argilline ingestion was significantly greater (p<0.01) than that without L-Arginine. Furthemore, an increase in left dorsal skin blood flow after 10 to 15 minutes bathing with L-Arginine was more marked than that without L-Arginine. The increasing ratio of blood flow after 15 minutes of right forearm bathing against pre-bathing value was significantly higher (p<0.05) in case with L-Argitme than that in its absence. These results suggest that the oral administration of L-Arginine accelerates thermal vasodilative effects during forearm bathing.