The regulation of aquaporin-2 (AQP2) water channel excretion in the collecting duct depends mainly on the action of vasopressin (AVP). Recently, however, other regulatory factors have been identified: atrial natriuretic factor, oxytocin and prostaglandins. In healthy volunteers (5 males, 5 females; mean age 23 ± 3 years) we therefore evaluated the effect of a stable analogue of prostacyclin-2 (PGI2), iloprost, on renal function and on the urinary excretion of AQP2 (U-AQP2). After 6 h of iloprost infusion, U-AQP2 increased from 0.8 ± 0.15 to 1.8 ± 0.2 pmol/mg creatinine (p < 0.001), while the urinary flow rate increased from 1.4 ± 0.2 to 1.8 ± 4 (p < 0.01). No significant change was found in the AVP serum concentration, with a basal value of 3.17 ± 0.12 vs. 3.15 ± 0.12 pg/ml after 6 h of prostacyclin infusion. All the values returned to pre-study levels after a recovery period of 6 h. In conclusion, the PGI2 analogue, iloprost, can induce U-AQP2 excretion independent of AVP.