Abstract: A method is described for determining the level of lead in blood and other types of samples. The level of lead is determined by using a lead-sensitive enzyme. As a first step, a native lead-sensitive enzyme in the sample is disabled. This step may be omitted if the sample is known not to contain any lead-sensitive enzymes. A quantity of lead-sensitive enzyme with known enzymatic activity is then added to the sample. The new enzymatic activity of the sample is then measured. Finally, the level of lead in the sample is determined from the measurement of the new enzymatic activity, which differs from the known enzymatic activity if lead is present in the sample.