The aim of this study was to compare the fall in transcutaneous oxygen tension (PtcO2) as an outcome measure during bronchial provocation with histamine, with changes in airway function measured by the squeeze technique in healthy infants and those with wheezing disorders. PtcO2 was measured during histamine challenge in 20 infants, aged 6-16 months, of whom 14 had recurrent cough or wheeze (lower respiratory illness, LRI), and 6 were healthy. All were symptom free at the time of testing. The minimum value of PtcO2 after each nebulization was compared with the minimum baseline value. The response to increasing concentrations of histamine was also assessed by measuring maximal flow at functional residual capacity (VmaxFRC) by the squeeze technique. The inhaled concentration of histamine causing a 30% fall in VmaxFRC was calculated to give the provoking concentration (PC30). Baseline VmaxFRC was lower in symptomatic infants (117 mL/s) than the normal infants (322 mL/s; P < 0.005), but the PC30 was not significantly different (7.7 and 5.7 g/L, respectively). There was no difference in baseline PtcO2 between the two groups. The infants with LRI had significant reductions in PtcO2 at both the final and preceding concentrations of histamine, whereas the normal infants had a significant and smaller reduction in PtcO2 only at the provoking concentration. Reduction in PtcO2 during bronchial challenge was a less sensitive index of bronchial response in healthy infants than in infants with a history of recurrent LRI.