During the winters of 1967/1968 and 1968/1969 a newly developed air pollution monitor was tried out in a field test. The sulphur dioxide concentration was continuously measured in the atmosphere of Eindhoven, a medium-sized town in the Netherlands. The town is characterized by cleanness in industry and hence the air pollution was expected to be low, especially after the large-scale change-over from the burning of coal and oil to the use of natural gas for industrial and domestic heating in the year preceding the beginning of the measurements. Generally, these expectations came true, with the exception of the high sulphur dioxide concentrations which sometimes occurred in easterly winds. They were in contrast with the relatively slight urbanization east of the measuring station. On this the hypothesis is based that high sulphur dioxide concentrations at Eindhoven may be caused by the German Ruhr area situated at 100 km distance. An analysis of the data suggests this influence. The transport of sulphur dioxide is promoted by strong winds and by either a stable atmosphere or a low-level inversion layer in the atmosphere. In addition to the influence of the Ruhr area on the sulphur dioxide concentrations there are indications of an influence of the industrial area of Antwerp. No influence from the industry of Rotterdam with its many oil refineries could be distinguished.