BACKGROUND Can plasmapheresis improve disease severity and lung function and reduce steroid doses in severe asthma patients dependent on oral corticosteroids? METHODS A pilot study with four asthma patients was undertaken using PEF (peak expiratory flow) symptom score, number of puffs of beta2-agonist, and dose of systemic steroids as disease variables. After at least an 8-week run-in, the patients were randomized to a crossover treatment regimen consisting of either 10 days of plasmapheresis or placebo treatment. Each treatment was succeeded by an 8-26-week follow-up period. RESULTS No patients achieved a significant effect of plasmapheresis treatment according to the established criteria, nor did anyone experience deterioration. CONCLUSIONS Removing humoral factors extensively over a 10-day period did not significantly influence the clinical condition of the four steroid-dependent asthma patients studied. Circulating humoral factors seem to be of little importance for the maintenance of the established chronic allergic inflammation in these patients. Plasmapheresis does not seem to be a treatment option for this patient category.