This survey was carried out in the molding of plastics and rubbers, in the "Professional Cancer Prevention Project" sponsored by the Lombardy region with the objective of developing and implementing protocols for evaluating exposure to carcinogens through the biological monitoring. The realities of molding the thermoplastic polymer ABS, rubber, and thermosetting plastics containing formaldehyde were examined. The carcinogenic substances identified in these processes were: 1,3-butadiene, acrylonitrile and styrene in molding ABS, polycyclic aromatic hydrocarbons (PAH) in molding rubber, and formaldehyde in molding the thermosetting plastics. Only for some of these substances biological indicators are available. The limited exposure to airborne chemicals in molding ABS and the intrinsic characteristics of biological indicators available for 1-3 butadiene have determined the non applicability of biological monitoring to this situation. The absence of a biological indicator of exposure to formaldehyde has made this situation not investigable. Exposure in the rubber molding was studied in 19 subjects applying the determination not metabolized PAH in urine. The levels of these indicators were similar to those measured in other groups of subjects without occupational exposure to PAH, confirming a low airborne contamination in this workplace.