The effects of the diuretic furosemide (CAS 54-31-9) 1 mg/kg bw i.v., of the angiotensin converting enzyme (ACE) inhibitor captopril (CAS 62571-86-2) 1 mg/kg bw p.o. and the prostaglandin synthesis inhibitor indometacin (CAS 53-86-1) 2 mg/kg bw p.o. on kidney function, salt and water excretion, the excretion of renal prostaglandins PGE2, PGF2a, 6-keto-PGF1a, thromboxane B2 (TXB2) and the plasma renin activity (PRA) were investigated on 29 neonatal piglets. Within 1 h, fuorsemide led to pronounced diuresis and natriuresis, to a rise of the glomerular filtration rate (GFR) (which ist low in neonatal pigs) by 1.8 times, increased the excretion of renal prostaglandins (especially the vasoconstrictor, thromboxane B2 (TXB2 and PGF2a) and raised the PRA significantly. Under captopril, the PRA rose significantly, whereas there was no unequivocal change in the excretion of renal prostaglandins. There was a pronounced decline of the sodium and potassium excretion in the urine with a fall in the concentrations of electrolytes in serum and of the hematocrit. Under indometacin, the excretion of all prostaglandins in the urine declined (this decline was most pronounced for PGE2). There was also a decrease in sodium excretion, whereas there was no significant change in PRA. It can be concluded from the results that the effects of the investigated drugs on the pig neonate kidney is at least partially attributable to an influence on hormonal factors.