1 We studied the effects of pre-treatment with oral indomethacin (25 mg four times daily for 3 days) on the pharmacokinetics, haemodynamics and diuretic properties of oral felodipine (10 mg single dose) in 12 healthy male volunteers using a placebo controlled double-blind four-way crossover protocol. 2 Felodipine with or without indomethacin pretreatment reduced standing diastolic blood pressure (P < 0.001) at 0.5 to 3.0 h after dosing compared with placebo or indomethacin alone. Systolic blood pressures during indomethacin treatment alone were consistently higher than the other three treatment groups (P < 0.01), presumably due to sodium and fluid retention. 3 Felodipine and felodipine plus indomethacin produced significantly greater excretion of urine and urinary sodium, but not of urinary potassium or creatinine when compared with placebo (P < 0.01) over an 8 h period.4 The pharmacokinetic parameters of felodipine (Cmax, tmax, tv2 and AUC), the concentration-response curves for blood pressure lowering effects, the reflex tachycardia, diuretic properties and side-effects profile of felodipine were not significantly altered by indomethacin pretreatment in normal volunteers.