Treatment of tuberculosis with rifampicin in patients with pre‐existing adrenal failure has been reported to induce adrenal crisis due to alteration of Cortisol metabolism by induction of hepatic mixed liver oxygenase enzymes. To determine whether mineralocorticoid metabolism is altered by rifampicin treatment, we established the pharmacokinetics of immunoreactive aldosterone. The metabolic clearance rate (MCR) and plasma half‐life of this material were measured before and after 6 days of rifampicin treatment (600 mg/day) in seven patients with Addison's disease due to tuberculosis. Antipyrine clearance and urinary 6‐β‐hydroxycortisol excretion was determined to demonstrate induction of the cytochrome P 450 dependent enzymes. Infusion of aldosterone at a constant rate of 0‐17 mg/h over 4‐5 h produced steady state concentrations after 2 h, with no difference before and after rifampicin treatment (mean ± SD, 1649 ± 144 vs 1586 ± 80 pg/ml, respectively). The disappearance curve of IR‐aldosterone from plasma was biexponential. No change could be observed in the plasma half‐lives (α‐phase 29 ± 1.9 min vs 30 ± 1.5 min, β‐phase 129 ± 3.2 minra126 ± 4.3min), the MCR (1‐47 ± 0.1 1/h/kg vs 1.46 ± 0.1 1/h/kg vs), and the volume of distribution (9.9 ± 1.9 vs 10.2 ± 0.3 1). The antipyrine half‐life decreased significantly from 12.2 ± 2.6 h to 7.6 ± 0.9 h (P± 0.05) with a rise in antipyrine clearance from 0.38 ± 0.07 to 0.80 ± 0‐23 ml/min/kg (Plt;0.05) and no change in the volume of distribution. Urinary excretion of 6‐β‐hydroxycortisol increased from 711 ± 130 μg/24 h before to 1670 ± 387/μg/24 h (P < 0‐05) after 6 days of rifampicin treatment with no changes in urinary free Cortisol excretion.