During the last decade, there has been a sharp increase in the number of tests routinely used to screen all volunteer whole blood donations for evidence of transfusion-transmissible infection. These measures have had a dramatic effect on improvements in transfusion safety, especially as far as hepatitis viruses and the human immunodeficiency virus are concerned. Although all blood donations are not routinely screened for evidence of possible transmissibility of cytomegalovirus, some are, since there is now a clearer understanding of the categories of patients in whom this infection must be avoided. Recent studies have also pointed to a role for leukocyte filtration of transfusion products as an alternative to donor screening for selected patients at risk of cytomegalovirus infection. With regard to other viruses, knowledge about the relevance of Epstein-Barr virus, human herpesvirus 6, and parvovirus to blood product safety is incomplete. Until their pathogenicity, if any, in transfusion recipients is known, recommendations about special handling of blood products because of concern for these viruses is premature.