In this study, the complexation rates of two new phosphinate H(4)dota (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) analogs, H(5)do3ap(PrA) and H(4)do3ap(ABn), and H(4)dota itself were compared under identical conditions (H(5)do3ap(PrA)=10-{[(2-carboxyethyl)hydroxyphosphoryl]methyl}-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid; H(4)do3ap(ABn)=10-{[(4-aminophenyl)hydroxyphosphoryl]methyl}-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). The biodistribution of their (111)In and (90)Y complexes in healthy rats was also studied. Unlike the observation obtained under "chemical" conditions where differences between the ligands were observed no such differences in complexation rates were found under radiochemical conditions. The ligands bind the radiometals similarly to H(4)dota. So, "chemical" formation kinetic data should be transferred into radiochemical conditions only with high care and "radiochemical" complexation experiments should be run as part of standard in vitro studies with new ligands considered as potential radiopharmaceuticals. Pharmacokinetic studies in rats showed similar distribution characteristics for both phosphinate H(4)dota analogs radiolabelled with (111)In and (90)Y when compared with that of the (111)In-H(4)dota complex. No specific uptake in any organ and tissue of rats was determined. The phosphinate complexes are not accumulated in calcified tissues.