Intracerebral injection of CH3Hg and CH3Hg complexed with glutathione (CSH), cys‐teine (cys), cysteinylglycine (cys‐gly), and homocysteine (homocys) resulted in differences in toxicity. Criteria based on neurological indices, mortality, and weight loss indicated that the cys‐gly complex of CH3Hg was significantly less toxic than CH3Hg or the other complexes. The other complexes of CH3Hg (CSH, homocys, and cys) were also found to be less toxic than CH3Hg. The selenium status of the animal did not seem to significantly influence the toxicity of CH3Hg and the complexes. While CH3Hg complexed to cys‐gly was significantly less toxic than CH3Hg alone, there were no differences observed in the CH3Hg half‐life values or in the distribution of these compounds in the kidneys, brain, liver, and blood. It was observed, however, that the CH3Hg‐cys‐gly complex had higher fecal excretion on d 3 and 4 following intracerebral injection.