1. The effects of chronically administered cicletanine (CICL), an antihypertensive and prostacyclin stimulating agent, on glomerular hemodynamics were evaluated after 30 (CRF-30) or 60 (CRF-60) days of chronic renal failure (CRF) induced by 5/6 nephrectomy in Munich-Wistar rats. 2. CICL administration (3 mg kg-1 day-1, N = 5) for 60 days did not modify glomerular hemodynamics of normal rats (control group). The CRF-60 group (N = 6) presented a significant increase in mean arterial pressure (MAP) compared with control (122 +/- 7 vs 98 +/- 2 mmHg, P < 0.05), which was attenuated by CICL (113 +/- 7 vs 122 +/- 7 mmHg). 3. Hyperfiltration and hyperperfusion were observed in both CRF groups after 30 (N = 5) but not after 60 days of CRF, 73.9 +/- 6.3 and 48.2 +/- 3.2 vs 36.8 +/- 2.6 nl/min for SNGFR and 200 +/- 17 and 147 +/- 8 vs 112 +/- 8 nl/min for QA in CRF-30, CRF-60 vs control group, respectively. However, glomerular hypertension was demonstrable for both CRF groups only after 60 days. CICL treatment starting 7 days prior to nephrectomy reduced the transcapillary hydraulic pressure difference (delta P) in both groups, 36 +/- 3 vs 30 +/- 2 mmHg (30 days) and 41 +/- 4 vs 34 +/- 2 (60 days), but did not significantly modify arteriolar resistances or glomerular hemodynamics, suggesting that the reduction in MAP in response to CICL may have been responsible for the decrease in delta P. CICL administration did not prevent the proteinuria or glomerular sclerosis associated with CRF. 4. The results suggest that the administration of CICL for 30 (N = 4) to 60 days (N = 7) was sufficient to prevent systemic hypertension associated with CRF but not to reduce the additional glomerular hemodynamic factors that participate in the progression of CRF.