Occupational exposure to styrene has been of special concern in Norway since the beginning of the 1970s, especially the exposure in the reinforced plastic industry. Campaigns have been carried out by the Norwegian Directorate of Labour Inspection and various measures have been set forth to reduce the workers' exposure to styrene. Alongside the campaigns, extensive monitoring programs were carried out. The measurement results are compiled in the database EXPO at the National Institute of Occupational Health (Norway). This article presents a statistical analysis of the measurement data to assess the occupational exposure to styrene in Norway since the 1970s. Results from 7,011 measurements carried out in 234 enterprises covering the period 1972-1996 are included in the database. The analyses show occupational exposure to styrene of 33.0 ppm (median) (mean: 49.4 ppm) for this period. The analyses show a decrease from a median of 62 ppm in the 1970s to 7.1 ppm in the 1990s. The analyses do not disclose any crucial impact from any single preventive measure implemented by the authorities to reduce exposure level. The reduction in the level is probably due to a contribution from different measures. The decline in the styrene exposure coincides with a similar reduction in other countries, and it may be that international concern and technical improvements in the manufacturing process have been an important factor in the exposure level reduction in the Norwegian plastic reinforced industry as well.