The influence of dopamine and droperidol on the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) was examined in twelve groups (N = 8) of male wistar rats using the double isotope method with a partially-shielded whole-body counter according to Oberhausen. No alterations of GFR and ERPF could be elicited in normovolaemic rats given dopamine 2--4 micrograns/kg/min (i.v.) alone or in combination with droperidol 0.3 mg/kg. The administration of 10 micrograms/kg/min dopamine alone was followed by a significant (p less than or equal to 0.05) reduction of the ERPF, this effect being abolished by the concomitant use of both drugs. In tourniquet shock dopamine administration or the combined use of dopamine and droperidol produced a significant rise in arterial blood pressure and the renal functions described above. The results in the present study indicate that dopamine infusions will be effective in the presence of froperidol.