To ascertain whether current screening procedures for human immunodeficiency virus (HIV) infected blood can be improved, a study of blood donors found by Mersey and North Wales Blood Centre to be HIV positive was made. In total 22 donors were identified, of which 16 were referred to the Department of Genito-Urinary Medicine (GUM) in Liverpool. Most (9/16) should have been excluded from donating because of recognized risk factors. However, in 7 cases no such identifiable factors were found. Although the risk of transfusion transmitted infection is small, there is an argument for testing donated blood for HIV RNA by nucleic acid technology.