A graphite furnace atomic absorption spectrophotometric assay, capable of accurately determining nanogram amounts of platinum in serum and ultrafiltrate, was developed. A sample serum or ultrafiltrate was acidified with nitric acid and heated to destroy the protein-platinum bond. A measured excess of ammonium 1-pyrrolidinedithiocarbamate was added, and the platinum complex was extracted into isopropylacetone. The extract was injected into the graphite furnace. The sample was dried, charred, and atomized using optimal conditions. The resulting absorbance was used to determine the platinum content.