Our recent work suggests limited uptake of unstabilized metal oxide nanoparticles via water into fish, however, some other studies have indicated such exposures can induce oxidative stress. To investigate tissue distribution and toxicity of titanium dioxide (TiO(2)) nanoparticles that may enter into fish, we conducted a series of injection studies. Rainbow trout (Oncorhynchus mykiss) were intravenously injected with 100 microg TiO(2) nanoparticles and the content of titanium in blood, brain, gills, liver, and kidney quantified at time points between 6 h and 90 days using inductively coupled plasma optical emission spectroscopy. Injected Ti was concentrated in the kidneys and remained there up to 21 days, however, there was evidence of clearance of TiO(2) at 90 days. Ti accumulation in the liver was 15 times lower than in the kidney with no apparent clearance. Using TEM we showed nanoparticles were localized in tissue vesicles surrounding the kidney tubules. In a second injection study, rainbow trout were injected with 100 microg TiO(2) and plasma samples from individual fish analyzed for total protein and creatinine content at time points between 6 h and 21 days to assess for possible effects on kidney function. No effect of TiO(2) on total plasma protein content or creatinine concentrations were found indicating that neither urine production nor glomerular filtration rate were affected. We conclude that in trout upon a single high dose exposure of TiO(2) nanoparticles via the bloodstream, TiO(2) accumulates in the kidneys but has minimal effect on kidney function.