Objective: To present an interim analysis of the effect of a home-based inter vention with low-income caregivers ofwheezing infants at risk for childhood ast hma on mediating variables. Method: Infants aged 9 to 24 months with 3 or more p hysician-documented wheezing episodes were randomly assigned to environmental s upport intervention (ES) (n = 90) or control (n = 91) groups. Nurse home visitor s intervened for 1 year to decrease allergen and environmental tobacco smoke exp osure and improve symptom perception and management. Assessments at baseline and 12 months included allergens in house dust, infant urinary cotinine levels, car egivers’symptom reports, quality of life, illness management, and quality of ca regiving. Medical records were coded for hospitalizations, emergency department visits, and corticosteroid bursts. Results: Within the ES group, cockroach aller gen levels were significantly reduced and there was a trend toward reduction in dog dander levels. Among infants with detectable urinary cotinine, levels were s ignificantly reduced in the ES group. Caregiver psychological resources modified the impact, and low-resource ES caregivers were the most strongly affected. As thma knowledge and provider collaboration improved significantly in the ES group . Neither reports of infant symptoms nor emergency department visits or hospital izations showed positive intervention effects. Number of corticosteroid bursts f or infants was significantly higher for the ES group. Conclusions: The Childhood Asthma Prevention Study intervention was effective in reducing several environm ental exposures and improving illness management. However, even with an intensiv e home-based intervention, we failed to reduce respiratory symptoms or medical use in the ES group relative to the control group, illustrating the difficulty o f changing the course of early asthma development among low-income infants. Objective: To present an interim analysis of the effect of a home-based intervention with low-income caregivers of wheezing infants at risk for childhood ast hma on mediating variables. Method: Infants aged 9 to 24 months with 3 or more p hysician-documented wheezing episodes were randomly assigned to environmental s upport intervention (ES) (n = 90) or control (n = 91) groups. Nurse home visitor s intervened for 1 year to decrease allergen and environmental tobacco smoke exp osure and improve symptom perception and management Assessments at baseline and 12 months included allerrgens in house dust, infant urinary cotinine levels, car egivers’symptom reports, quality of life, illness management, and quality of ca regiving. Medical records were coded for hospitalizations, emergency department visits, and corticosteroid Results: Within the ES group, cockroach aller gen levels were significantly reduced and there was a trend toward reduction in dog dander levels. Among infants with detectable urinary cotinine, levels were s ignificantly reduced in the ES group. Caregiver psychological resources modified the impact, and low-resource ES caregivers were the most strongly affected. As thma knowledge and provider collaboration improved significantly in the ES group. Neither reports of infant symptoms nor emergency department visits or hospital izations showed positive intervention effects. Number of corticosteroid bursts f or infants was significantly higher for the ES group. Conclusions: The Childhood Asthma Prevention Study intervention was effective in reducing several environm ental exposures and suggesting illness , even with an intensiv e home-based intervention, we failed to reduce respiratory symptoms or medical use in the ES group relative to the control group, illustrates the difficulty of changing the course of early asthma development among low-income infants.