1. The renal responses to the dipeptides γ-l-glutamyl-l-dopa (gludopa) and γ-l-glutamyl-l-tyrosine (glutyrosine) were compared when given intravenously in six normal male volunteers.
2. Gludopa is natriuretic and diuretic at a dose of 25 μg min−1 kg−1. At the same dose, glutyrosine had no effect on the volume or sodium content of the urine.
3. There was a 400-600-fold increase in urine dopamine output after gludopa; there was no conversion of glutyrosine to dopamine.
4. Gludopa significantly inhibited plasma renin activity, whereas with glutyrosine there was a non-significant increase.
5. Gludopa is a potent pro-drug for renal dopamine production and exerts natriuretic and hormonal effects. Glutyrosine appears to be inactive. The results support the contention that circulating l-dopa is the important physiological precursor for renal dopamine.