1H nuclear magnetic resonance has been used to determine the effect of acute iv administration of the arginine vasopressin analog 1-(3-mercaptopropionic acid)-8-D-arginine vasopressin monoacetate (ddAVP; 2 micrograms) on renal medullary trimethylamine (TMA) levels in human volunteers. In subjects deprived of food and water for 15 h, urine osmolality (Uosm) was 889 +/- 47 mosmol/kg and had not changed significantly 3 h after ddAVP administration. Medullary TMA did not change significantly over 3 h after ddAVP. In a second group of subjects who were well hydrated, acute ddAVP infusion increased Uosm from 203 +/- 63 to 421 +/- 47 mosmol/kg in 3 h (P < 0.05). However, medullary TMA did not change significantly over this time period. These results indicate that ddAVP, and presumably arginine vasopressin, do not acutely influence medullary TMA levels, and they support the view that results previously reported for animal and isolated cell systems are also applicable to human physiology.