This paper describes the preparation of alizarin (1,2-dihydroxyanthraquinone) and alizarin red S (sodium 1,2-dihydroxyanthraquinone-3-sulfonate) labeled with Ga-68, which is obtained from a new high-yield Ge-68 leads to Ga-68 generator. The uptake of Ga-68 alizarin by liver and spleen RES was studied in rats, dogs, and human, and amounted to 80-85% of the administered dose within 5 min after i.v. injection. Gallium-68 alizarin red S was preferentially accumulated in the renal parenchyma to an extent of 70% within 2 hr after i.v. administration. Both substances combine simple and fast preparation with the potential advantages of positron scintigraphy. Complete labeling of 1 mCi Ga-68 was achieved by 100 micrograms of each compound, amounts that are without any known measurable harm to humans (LD50 alizarin red S for i.v. injected mice = 70 mg/kg (8); LD50 alizarin for i.p. injected mice > 120 mg/kg (18)).