We have demonstrated that the lysosome associated membrane protein (LAMP-1) is elevated in plasma from approximately 70% of lysosomal storage disorder patients. As part of the development of a newborn screening program for lysosomal storage disorders we have developed a first tier screening assay based upon the level of LAMP-I in blood spots taken from newborn Guthrie cards. To determine the effectiveness of the first-tier marker a prospective pilot Guthrie neonatal screening program for the identification of LSD was commenced in April 1998. Prior to commencement of the pilot program ethical approval was obtained and information leaflets regarding the neonatal screening of LSD were distributed to parents at the time of their infant's Guthrie collection. The LAMP-1 assay utilizes a chicken polyclonal and a mouse monoclonal in a sandwich time resolved fluorescent immunoassay. LAMP-1 blood-spot calibrators and quality control specimens were developed and shown to be stable and reproducible. To date 11,183 infants have been screened using LAMP-1. The population distribution is described with a median and 98th percentile of 220pg/l whole blood and 483microg/l whole blood respectively. Acceptable CV% for intra and inter assay of 8.9% and 10% respectively were obtained.