In the present medical practice a poisoning by lead is usually proved by measuring the concentration of Pb (II) ions in blood and urine and by the determination of d-aminolevulic acid (ALA) as well as by a semiquantitative determination of the porphyrines content in urine. The above analytical procedures are time-consuming and relatively expensive. The present communication describes the procedures used for obtaining independent analytical results in following the detoxication of the organism after a lead poisoning. It has been found that the quantity of Pb(II) ions determined in urine and blood and that of d-aminolevulic acid and of porphyrines in urine are not independent. A correlation was e.g. found between the porphyrine and the d-aminolevulic acid content. Thus the determination of one of last-mentioned substances is superfluous. The correlation analysis made it possible to propose a simplification and an acceleration of following the detoxication process in a patient.