Metal chelate formation between diethylenetriaminepentaaceticacid (DTPA) and Cu(II), Ni(II), Co(II), Zn(II), Mn(II) and Ca(II) ions was investigated by potentiometric and spectrophotometric procedures. The existence of three 1:1 metal chelates having the formulas M(II)DTPA, M(II)HDTPA and M(II)H2DTPA, as well as a binuclear complex, M2(II)DTPA, has been shown on the basis of these data. Equilibrium