To characterize trace metal cycling in marine systems as mediated by heterotrophic pro- tists, we conducted a series of laboratory experiments in 2-organism model systems consisting of bac- teria and protistan grazers. Trace metal isotopes ( 59 Fe and 234 Th), 14 C, and bulk organic carbon mea- surements were used to follow the chemical transformation of bacterial carbon and associated trace metals by several different grazer species. Results indicate that grazers were able to cause reparti- tioning of Th and regeneration of Fe from bacterial prey into the dissolved phase (<0.2 µm), even in particle-rich laboratory cultures. For both Th and Fe, protist grazing led to the formation of relatively stable dissolved and colloidal metal-organic species. Metal/carbon ratios of the particle pool in some model systems with grazers were significantly altered, indicating a decoupling of trace metal and organic carbon cycling through the grazing process. Different protist species exhibited substantial variation (up to a factor of 10) in their ability to quantitatively remobilize trace metals from bacterial prey. The implications of these findings for trace metal cycling in marine systems are discussed.