Many reports have shown bacterial contamination of nebulizers used by patients with cystic fibrosis (CF) at home. At the Stockholm CF centre we recommend dismantling the equipment, washing, rinsing and drying it after each use, and disinfecting it once daily by boiling water or by 2% acetic acid followed by drying without rinsing. We studied whether patients comply with these recommendations and whether they are sufficient to prevent bacterial contamination. Nebulizers from 49 CF patients were investigated, 21 of whom are chronically colonized with Pseudomonas aeruginosa and one with Burkholderia cepacia. All patients were visited at home. Thirty-nine patients (79%) disinfected their equipment after the latest use in accordance with our recommendations. Thirty-eight pieces showed no, or only scanty, growth of micro-organisms belonging to the normal oropharyngeal flora. A moderate growth of alpha-streptococci was observed from a further five pieces. Four of these had not been cleaned after the latest inhalation occasion, and one was visibly dirty. Pseudomonads were observed from three pieces; two of these had been disinfected by boiling water and one by acetic acid, followed by rinsing in tap water. All three had been inadequately dried. Pseudomonads could not be cultured simultaneously from the sputum of these three patients. In conclusion, most patients comply with our cleaning and disinfection recommendations and these recommendations appear satisfactory in preventing bacterial contamination.