In a newborn screening program for abnormal hemoglobins, 91 infants were found to have hemoglobin AS or AC. Their parents were informed and offered genetic counseling, but only 35% accepted. We tested parents' knowledge of sickle disorders before and after the session. The tests were repeated when their babies were 4 to 8 months old; parents of babies with normal hemoglobin and those with sickle trait who had not been counseled were also tested at this time. Parents who received counseling showed an increase in knowledge and retained it until the second interview although 27% did not recall the original session. Uncounseled parents of "trait families" also had knowledge of the condition; in general, trait families knew more about the condition than normals' families. Newborn hemoglobin screening programs prove helpful for certain families but not necessarily for all who may be eligible.