Aim: In this study, we describe the biodistribution of CYT-6091, a colloidal gold (Au)-based nanomedicine that targets the delivery of TNF-α to solid tumors. Materials & methods: A single intravenous injection of CYT-6091 coated with 5 µg TNF-α was given to human prostate tumor-bearing or naive (without tumor) nude mice. Tissues were harvested and analyzed at specific time points for Au nanoparticles by atomic emission spectroscopy and TNF-α by ELISA. Results: The two constituents of CYT-6091, TNF-α and Au, exhibited different behavior in blood, with TNF-α showing a faster decay than the Au nanoparticles. Between 0 and 4 h after injection, TNF-α showed a preferential accumulation in the tumor. Au was observed to accumulate preferentially in the liver between 4 and 12 h, and showed some clearance over time (4 months). Conclusion: These data suggest that CYT-6091 delivers TNF-α preferentially to the tumor and that upon TNF-α degradation, the liver takes up Au, which is cleared slowly over time.