[240][241][242][243]. A simple method for the quantitative analysis of urinary delta-aminolevulinic acid to evaluate lead absorption. A procedure is given for the rapid, quantitative determination of urinary delta-aminolevulinic acid (ALA). Interfering substances are removed by n-butanol extraction. After pyrrole formation with ethyl acetoacetate, Ehrlich's reagent is added to produce the chromophore, which is then extracted with chloroform and measured spectrophotometrically or by comparison of the depth of colour with standard colour solutions. The recoveries were about 91 % and the results agreed well with those obtained using ionexchange column chromatography (r = 0 985). This assay is simple, dependable, and suitable for large-scale screening of industrial workers exposed to lead poisoning, because the critical level of urinary ALA (20 mg./l. urine), which indicates dangerous lead absorption, gives a convenient absorbance.

A series of 44 workers occupationally exposed to lead and 79 habitants naturally exposed to lead was investigated in order to define more clearly the clinical and biochemical criteria of lead exposure after grouping them into five according to the degree of lead exposure and also to the clinical evidence.

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A rapid, inexpensive and simple method using Tetrahymena pyriformis has been