Introduction: Drugs used in asthma or COPD exacerbation are delivered to the lungs by inhalation. This is facilitated, among other factors, by the use of dry powder inhalers (DPIs). Lung deposition from DPI depends predominantly on peak inspiratory flow (PIF). The aim of the study was to asses the variability of PIF generated by patients using different types of DPI inhalers during asthma or COPD exacerbation and to trace possible relationships between PIF value and some spirometric values., Material and Methods: There were 28 patient fulfilling inclusion criteria, among them 17 (4 women) were suffering from COPD and 11 (8 women) from asthma. Spirometry, PEF and PIF measurements were performed in the first and the last day of hospitalisation. Peek inspiratory flow was obtained using In-Check DIAL - a device which simulated airflow resistances equivalent to Turbuhaler, Diskus and Aeroliser respectively., Results: The significant improvement in PIF was observed only in patients with COPD. There were no statistically significant correlations between PIF and both FEV1 and PEF except those in the first day of hospitalization in COPD patients (r = 0.66-0.81). Optimal PIF was achieved in all patients only with Diskus., Conclusions: Measurements of peek inspiratory flow are useful in choosing the most suitable DPI for patients with COPD and asthma exacerbations. We conclude that in those patients, PIF measurement should complement a standard spirometry.