The purpose of the study was to analyze the respiratory-dependent intraarterial blood pressure variations (pulsus paradoxus, PP) in intensive care unit patients with obstructive and restrictive pulmonary disease, and to evaluate the usefulness of PP for assessment of disease severity. One-minute paper recordings of arterial blood pressures, left atrial pressures (LAP, 16 patients), breathing cycles, and electrocardiograms (ECG) were taken in 54 nonintubated children. There was a close relationship between systolic and diastolic blood pressure variations (r = 0.92). The mean coefficient of variation of PP was 18.4% (SD 11.6%). The relationship between respiratory dependent LAP fluctuations (Delta LAP) and PP was logarithmic. PP correlated significantly with a respiratory severity score (RSS: wheeze, oxygen requirement, heart rate, arterial partial pressure of carbon dioxide) in a subgroup of 16 asthmatics (r = 0.66, P = 0.005); wheeze score was the only true independent determinant of RSS (multiple regression). In the nonasthmatics with restrictive lung disease, the correlation coefficient for the association between PP and RSS was 0.34 (P = 0.08), with a significant univariate correlation between PP and wheeze score (r = 0.62, P = 0.001). We conclude that PP correlates significantly with wheeze in obstructive and restrictive disease. PP is a valuable clinical sign of disease severity in patients with wheeze as clinical manifestation of obstructive airway disease. The relationship between Delta LAP and PP confirms the finding that an increase in PP is associated with a rise in left atrial transmural pressure.