The objective of this study was to determine the relationship between oxygen saturation (Sao2) and traditional clinical assessment measures in infants and young children presenting as outpatients with acute wheezing. To accomplish this, Sao2 before and after medication was compared in a post hoc analysis with the clinical response to treatment (respiratory rate and a standardized index of respiratory distress) in children who participated in a randomized, placebo controlled medication trial. The study was done in a pediatric emergency department and outpatient clinic, and the participants were 74, full-term previously well infants and young children, aged 1 to 36 months (mean age 16.1 months), presenting with acute wheezing and participating in the randomized trial. The results showed that Sao2 was found to be inversely correlated with both respiratory rate (r = -0.29, P < or = 0.05) and an index of respiratory distress (r = -0.36, P < or = 0.01) prior to medication but not afterward. There was no significant difference in Sao2 when infants, who had a clinical response to treatment based on a priori criteria, were compared to nonresponders (mean difference per patient: responders = 0.86% vs nonresponders = 0.79%, P = 0.51). This was due to a large amount of individual variability in postmedication Sao2 in both groups. We conclude that, before therapy, there are only weak correlations between SaO2 and both respiratory rate and an index of respiratory distress in acutely wheezing infants and children. After therapy, young children can appear clinically improved but measured oxygen saturation may be variable and not correlated with traditional clinical assessment measures.