A concise assessment of the risks to human health posed by exposure to methyl methacrylate, a synthetic chemical used primarily in the production of cast acrylic sheet, acrylic emulsions, moulding and extrusion resins, and several consumer and medical products, including dental prostheses, surgical bone cements, and orthotic shoe inserts. The document is part of a new series of brief reports aimed at the characterization of hazards and dose-response for exposures to selected industrial chemicals. With this goal in mind, documents in the series focus on studies and findings considered critical for risk characterization. Studies of environmental behaviour indicate that methyl methacrylate is emitted mainly to air, does not persist in the atmosphere, and is not expected to contribute to depletion of the ozone layer. Inhalation is identified as the principal route of human exposure. The general population may be exposed to methyl methacrylate through the use of paints, varnishes, lacquers and other consumer products. In animal studies, methyl methacrylate shows low acute toxicity. The principal effect observed with low doses was irritation of the nasal cavity. Higher doses were associated with adverse effects on the kidney and liver. Well-designed studies indicate that the chemical has no adverse effects on development and is not carcinogenic. In humans, methyl methacrylate is a mild skin irritant and has the potential to induce skin sensitization in susceptible individuals. Although occupational asthma associated with exposure has been reported, evidence that methyl methacrylate is a respiratory sensitizer was judged inadequate. Evidence from epidemiological studies of carcinogenic risk in humans was considered inconclusive. On the basis of toxic effects observed in inhalation studies in animals, the report established a tolerable daily intake of 1.2 mg/kg body weight.