In order to obtain further informations on the mode of action of Al, we carried out lasermicroanalytical determinations (LMA) of Aluminium (Al) on different parts of lumbar vertebrae in 54 non-nephrectomized rats and 54 ones 5/6 nephrectomized which were divided in 3 groups. The animals were treated with solutions of physiological NaCl in the control group (0.25 ml/100 g b.w.) and different Al-doses (0.05 and 0.5 mg/kg b.w.) intraperitoneally and daily for 4, 8, and 12 weeks. The results were compared with those of histochemical Al-detections by the method of IRWIN (1955). Lumbar vertebrae of the non-nephrectomized rats in the control group did not contain Al by LMA- and histochemical determination investigated in all the time intervals. Al-doses of 0.05 mg/100 g b.w. induced only a positive Al-proof 12 weeks after the beginning of the injections in the 5/6 nephrectomized animals by LMA, whereas Al-doses 10 times higher effected an Al-deposit of different concentration in the substance compact and substance spongioid of the lumbar body of vertebrae from the 4th week in the 5/6 nephrectomized and the 8th in the non-nephrectomized rats. The sensitiveness of the Al-detection by LMA was higher in comparison with the histochemical procedure, and an Al-accumulation in the lumbar vertebrae of the 5/6 nephrectomized rats is distinctly earlier than in those of non-nephrectomized animals.