1) The laboratory has spent considerable time and effort developing a first generation standard for the quantitation of HIV RNA in plasma. Several plasma and serum specimens from the CBER repository, harboring viruses of clade B origin, were evaluated by the Roche PCR assay and the Chiron branched DNA assay as well as 2 in-house assays. A specimen with a high titer of HIV RNA was identified and the copy number determined. Serial dilutions of this plasma specimen will be made available to kit manufacturers for their use in proficiency panels in developing test kits. We are presently collaborating with the NIBSC and the WHO to develop international reference reagents for a variety of blood borne viruses including HIV, HCV, HBV, Parvovirus B19 and HAV. 2) In molecular epidemiologic studies, virus isolated from long term non progressors (LTNPs) of HIV infection, are being characterized by viral load measurements and nucleotide sequencing using a variety of assays for these purposes. Isolates representing other subtypes of HIVare also being characterized by these methods. These studies should assist us in the evaluating the molecular epidemiology of HIV infection. In other studies, genetic sequencing has been performed on a variety of HIV-2 and HTLV-II isolates in order to determine the heterogeneity of these viruses. Our results indicate that most of the isolates from Spain belong to the subtype IIb4, commonly found in Southern Europe.