The distribution of low-molecular-weight, chromium-binding substance (LMWCr) and high-molecular-weight, chromium-binding substance (HMWCr) in the organ cytosol were analyzed by means of Sephadex G-25 gel filtration, after a single i.p. injection of K2Cr2O7 (280 mumol, Cr/Kg) to mice (male dd, 23 +/- 2 g). The amount of Cr in LMWCr per mouse was highest in the liver (83 micrograms), followed by those in the kidney (10 micrograms) and other organs (3-1 micrograms), with lesser amounts of Cr in HMWCr in all the organs. In these organs LMWCr was found to bind 3-28 times the amount of Cr to that in the in vivo binding after the in vitro incubation with K2Cr2O7 at 37 degrees C, showing a high Cr binding capacity of the substance. No inductive formation of LMWCr was observed in the liver even after daily repetitive administration of Cr (150 mumol/Kg, 4 days). Time course studies on the liver and the kidney of mice injected with K2Cr2O7 showed no difference in the accumulation of Cr in LMWCr and in the ratio of Cr in LMWCr to that in HMWCr between the organs at intervals of from 5 min to 24 hr after the injection. The comparative affinity of Cr(III) for LMWCr and for the serum proteins decreases in the order LMWCr, transferrin, albumin. The transfer of Cr from LMWCr to albumin and vice versa was almost negligible. However, significant amounts of the metal transfer was found from LMWCr to transferrin and vice versa, and from albumin to transferrin. These findings suggest that LMWCr is distributed widely in the body and it quickly binds invaded Cr in stable form at an organ site, especially in the liver, with participation of albumin or/then transferrin. This supports the hypothesis that LMWCr plays a large role in Cr detoxification.