The effects of the blood plasma proteins albumin (67 kDa) and transferrin (80 kDa) on the determination of Au and Pt, respectively, by ICP-MS using direct injection nebulization (DIN) or conventional pneumatic nebulization (PN) have been investigated. Detection limits using DIN were determined to be 0.6 pg (0.03 µg l^–1) and 1.6 pg (0.08 µg l^–1) for ¹⁹⁵Pt and ¹⁹⁷Au in 1.0 µmol dm^–3 solutions of transferrin and albumin, respectively, in 0.1 mol dm^–3 TRIS buffer. Precisions were high, ca. 0.5% over the range 1–100 µg l^–1. Calibrations were obtained with excellent linearity, and there was a wide linear dynamic range of four orders of magnitude with little interference from the protein. The binding of the anti-arthritic compound triethylphosphine gold(I) chloride (Et₃PAuCl) to albumin at various Au:albumin molar ratios was investigated using DIN-ICP-MS. It was concluded that DIN-ICP-MS is an improved method for determination of Au and Pt in the presence of proteins and therefore potentially valuable in pharmacological studies.