A conjugate of human albumin (HA) and 2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (p-SCN-Bn-DOTA) insoluble in aqueous medium at a pH of 3-8.5 and whose IR spectrum shows an absorption at about 700 cm−1 is described; a complex is further described consisting of a conjugate of HA and p-SCN-Bn-DOTA (HAC) according to claim 1 or 2 and a radioactive isotope of an element selected among the group consisting of P, Sr, Rh, Pd, I, Sm, Er, Au, At Bi, In, Lu, Y, Re, Cu and Ag, as well as procedures for preparing said conjugate and said complex as well as the use of such conjugate in the identification of mammalian neoplastic lesions by the R.O.L.L. methodology (“Radioguided Occult Lesion Localization”).