Screening for phenylketonuria (PKU) and congenital hypothyroidism (CH) is of concern to parents, physicians, and public health professionals. Parents have an abiding interest in a predictive activity that can prevent disease in their offspring. Physicians and their consultants must counsel parents and interpret a positive screening test. Public health personnel are concerned with the specificity and sensitivity, efficiency, and effectiveness of newborn screening. The Committee on Genetics has previously published recommendations on newborn screening for PKU and CH.1 Further recommendations are required because PKU and CH screening are widely practiced joint procedures in the newborn and because most full-term newborn infants are now being discharged from North American nurseries within the first three days after birth. This new practice is likely to have an effect on the validity of newborn screening and on screening for PKU, in particular. A recent statement from the Committee on Fetus and Newborn (Pediatrics 65:651, 1980) addressed the problem of so-called "in and out deliveries." However, the statement was ambiguous on the issue of whether such infants should be screened routinely on the initial discharge from the nursery. The Committee on Genetics believes that all infants, regardless of age, should be screened for PKU and CH at discharge from the nursery. The Committee believes that screening is not the equivalent of diagnosis; some cases of PKU and CH will inevitably be missed by screening. Whereas an important reason for missed cases may be the biology of the target disorders, none should slip through the screening mesh because of flaws in the program and its components.