In water loaded (5 ml/100 g) unanesthetized rats. nitrendipine (NT), nimodipine (NM) and nisoldipine (NS) (5 mg/ kg, i.p.) caused significant (P < 0.01) increase in water and Na+ excretion. However, there was no significant increase in K+ excretion after NT, NM and NS administration. NS was more potent in increasing excretion of water load as compared to NT and NM. The glomerular filtration rate as assessed by creatinine clearance, was significantly (P < 0.01) increased in NT, NM and NS (5 mg/kg, i.p.) treated groups as compared to control. The mean creatinine clearance values after NT, NM and NS were 26.95 +/- 0.35, 22.11 +/- 0.72 and 28.13 +/- 0.95 respectively as compared to 22.19 +/- 0.51, 18.77 +/- 0.42 and 22.97 +/- 0.60 in corresponding control groups. The results of the study suggest that in addition to other effects, NT, NM and NS have a selective inhibitory effect on Na+ handling mechanisms in the nephron.