A screening questionnaire for selecting infants requiring careful developmental supervision, based on the Gesell Developmental Schedules, was tested. Public health nurses completed this on 901 infants approximately 40 weeks of age. Screening efficacy was measured against a Gesell Developmental Examination done by a pediatrician. The questionnaire underscreened 29% of the infants the pediatrician called abnormal. No case of serious neurologic abnormality and only 2 with intellectual defect were missed. When the pediatrician used the observations of the examination to complete the questionnaire the underscreening was only 7%. No serious neurologic or intellectual defect was undetected. Specific changes which could reduce the underscreening were suggested.