1. The systemic effects of inhaled fluticasone propionate (FP), administered via Diskhaler, on the hypothalamo-pituitary-adrenal (HPA) axis were assessed primarily by measuring plasma cortisol at frequent intervals for 20 h after drug administration. 2. FP showed a dose-related suppression of plasma cortisol measured as area under the plasma cortisol vs time curve (AUC 0-20). The cortisol suppression (expressed as % fall from placebo) was 8, 19, and 28% for single doses of 250 micrograms FP, 500 micrograms FP and 1000 micrograms FP, respectively. A single dose of budesonide, 800 micrograms (via Turbuhaler), resulted in a 16% cortisol suppression. The cortisol suppression for all three single doses of FP, and for the single dose of budesonide, was statistically significantly different from placebo. 3. Repeated dosing of FP (1000 micrograms twice daily for 3.5 days) resulted in a more marked plasma cortisol suppression; a fall of 65% from placebo (AUC FP 1000 mg twice daily vs AUC placebo, P < 0.001). 4. In a well-controlled study in healthy volunteers, inhaled FP, in therapeutic doses, was shown to exhibit systemic effects which appear to be more pronounced after repeated dosing.