The present study describes for the first time a procedure for the radiolabeling of fullerene (C(60)) nanocrystals (nanoC(60)) with Na (125)I, as well as the biodistribution of radiolabeled nanoC(60) ((125)I-nanoC(60)). The solvent exchange method with tetrahydrofuran was used to make colloidal water suspensions of radiolabeled nanoC(60) particles. The radiolabeling procedure with the addition of Na (125)I to tetrahydrofuran during dissolution of C(60) gave a higher radiochemical yield of radiolabeled nanoC(60) particles in comparison to the second option, in which Na (125)I was added after C(60) was dissolved. Using photon correlation spectroscopy and transmission electron microscopy, (125)I-nanoC(60) particles were found to have a crystalline structure and a mean diameter of 200-250 nm. The (125)I-nanoC(60) had a particularly high affinity for human serum albumin, displaying 95% binding efficiency after 1 h. Biodistribution studies of (125)I-nanoC(60) in rats indicated significant differences in tissue accumulation of (125)I-nanoC(60) and the radioactive tracer Na (125)I. The higher accumulation of radiolabeled nanoC(60) was observed in liver and spleen, while accumulation in thyroid, stomach, lungs and intestines was significantly lower in comparison to Na (125)I. In addition to being useful for testing the biological distribution of nanoC(60), the described radiolabeling procedure might have possible applications in cancer radiotherapy.