Skin atrophy has been observed after prolonged use of inhaled corticosteroids. We therefore studied the effect of inhaled budesonide and nedocromil in patients with asthma on concentrations of procollagen propeptides in suction blister fluid reflecting skin collagen synthesis in vivo. Both types I and III procollagen propeptide concentrations decreased significantly after 6 wk of either 1,600 micro g/day (n=10) or 400 micro g/day (n=9) of inhaled budesonide but not in control subjects using inhaled nedocromil 16 mg/day (n=9). The reduction in mean propeptide concentrations ranged from 39 to 63%; the effects of the two budesonide doses did not differ significantly. Thus, even a low dose of inhaled corticosteroid represses skin collagen synthesis within a relatively short period.