In seven recurrently wheezy infants who were found to be histamine-responsive during bronchial challenge, changes in oxygenation (by oximeter and transcutaneous PO2 electrode) and carbon dioxide tension (by transcutaneous PCO2 electrode) were concurrently measured. The histamine challenge consisted of doubling concentrations administered by nebulizer for 1 min at 5-min intervals, up to a maximum concentration of 8 g/L. The response was determined from maximum expiratory flow using a squeeze technique. Significant mean reductions in transcutaneous oxygen tension of 0.9 +/- 0.7 kPa and 1.5 +/- 0.9 kPa were seen respectively at half the provoking concentration and at the provoking concentration of histamine that caused a significant reduction in maximum expiratory flow rates. The reduction in oxygen saturation of 4.8 +/- 3% was also significant at the provoking concentration. No significant change in transcutaneous carbon dioxide tension was seen. These results suggest that acute histamine-induced airway obstruction causes significant ventilation/perfusion disturbance in wheezy infants. Oxygen monitoring should be performed during bronchial challenge tests in infancy.