A study of the health hazards for workers exposed to styrene in the Dutch glass-reinforced plastics industry was undertaken. The open mould techniques of filament winding, spraying and hand laminating were chosen for study because exposure of workers using them was expected to be high. Occupational hygiene surveys were conducted in four plants. In addition to measurements of exposure, data on health complaints were collected. In 12 smaller plants exposure was estimated in walk-through surveys. The results show that although most of the plants had implemented control measures such as ventilation and extraction, the levels of exposure constituted a health risk. Time-weighted average concentrations for workers involved in filament winding ranged from 134 to 716 mg m−3, for those who were spraying from 48 to 602 mgm−3 and for those laminating manually from 18 to 538 mgm−3. The ‘no-adverse-effect level’ based on effects observed in man is considered to be 105 mg m−3, and the acute subjective health effects experienced by the population studied supported this value. To rduce exposure to below 105 mg m−3, control measures should combine engineering with codes of practice adapted to the particular process or processes employed.