Tc-99(m)-p-aminohippuric acid (Tc-99(m)-PAH) is a new renal radiopharmaceutical prepared from a lyophilized kit by the addition of sodium pertechnetate ((NaTcO4)-Tc-99-O-m. Each vial contains PAH, the calcium trisodium salt of diethylenetriamine pentaacetic acid (CaNa(3)DTPA) and stannous chloride (SnCl2. 2H(2)O) in an inert atmosphere. It is a stable radiopharmaceutical with high radiochemical purity ( GT 95%). Its protein binding is very similar to that of I-131-OIH, but it is hydrophilic in character. Animal studies using Tc-99(m)-PAH have indicated that it provides renal images of satisfactory quality with no external background. Despite its almost identical radiochemical purity and HPLC analysis results to Tc-99(m)-DTPA, Tc-99(m)-PAH is rapidly secreted by the kidneys in a manner consistent with tubular secretion, as confirmed by rat probenecid studies, whereas Tc-99(m)-DTPA is excreted by glomerular filtration. The pharmacokinetic parameters of Tc-99(m)-PAH (t(1/2(alpha))) = 2.5 min, t(1/2(beta)) = 41.7 min, Cl = 5.22 ml . min(-1), K-el 5.1 x 10(-4) min(-1)) differ from those of Tc-99(m)-DTPA. Evaluation of Tc-99(m)-PAH in two human volunteers confirmed its good renal characteristics: rapid disappearance from the vascular system, high uptake in kidneys followed by its very fast elimination, and low residual activity 20 min after its intravenous administration. (C) 1999 Lippincott Williams and Wilkins).