Dr. Albertini and colleges organized a group of researchers from the United States, Czech Republic, The Netherlands, and the United Kingdom to determine whether biomarkers in the blood and urine of workers exposed to butadiene in occupational settings correlated with their personal exposure. Samples were collected from male workers employed either in a plant that used butadiene and styrene to produce rubber polymer in Prague. They also collected blood and urine from male administrative workers at the plant who had no direct occupational exposure to butadiene and served as control subjects. Each worker's personal exposure to butadiene in air was measured occasionally using a small air sampler attached to his clothes for a sixty day period. The investigators focused their investigation on two types of biomarkers. The first type comprised biomarkers of exposure that were chosen specifically to indicate the level of butadiene in the body that resulted from an exposure. The second type of biomarker comprised biomarkers of effect, including gene mutations and structural changes in chromosomes.