In Finland, potatoes are often grown in soils with low pH (pH < 5.5). As the high pH is thought to favor the occurrence of common scab, growers have avoided liming, which has lead to the acidification of soils. In acidic conditions, soil calcium content is low and availability to plants of many essential nutrients such as phosphorus is poor. Potato common scab is a disease that causes great financial losses in potato production. It is caused by two bacterial species, Streptomyces scabies and S. turgidiscabies. Control of common scab is difficult as there are no chemical control methods available. Traditionally, management of common scab has based on cultural practices such as maintaining low soil pH. However, in recent years these methods have proved less effective, probably due to the infestation of fields with S. turgidiscabies, which is tolerant of low pH, and an increase in the numbers of S. scabies strains adapted to acidic conditions. Therefore, new strategies for the control of this disease are needed. Use of slags in agriculture for liming and as fertilizer has a long tradition. The aim of this study was to investigate if converter and blast furnace slags produced by the steel industry could be used in potato production to raise soil pH and improve availability of nutrients to plants without increasing the risk for common scab. The effect of slags on soil pH and nutrients as well as potato growth and yield, with a special emphasis on common scab, was investigated in a four year study in 2004-2007. The study was carried out as a field experiment using slags from Rautaruukki Corporation steel works in Raahe or Koverhar. Different rates of converter (5, 10, 50 t/ha) and blast furnace (6, 10, 60 t/ha) slags were applied in the spring 2004 and their effects on three successive potato crops of cvs Sabina (2004) and Van Gogh (2005 and 2006) were recorded. In general, the slags increased effectively soil pH and nutrient levels on the first growing season after the amendments were made. Converter slag raised the soil pH and soil calcium content more effectively than blast furnace slag. In contrast, due to its higher magnesium content, blast furnace slag increased the soil magnesium level. On two subsequent years, soil pH and nutrient levels decreased and the differences between the rates and slag types were reduced. However, still four years after the applications, the effect of the highest rates of both converter (10 and 50 t/ha) and blast furnace slags (60 t/ha) on soil pH and soil calcium content was evident. Converter slag increased also the tuber calcium content. The rates of slags normally used for liming (5-12 t/ha) did not affect the crop growth or the quantity or quality of the tuber crop. However, the highest rate of converter slag tested (50 t/ha) had a tendency to delay the crop growth during the first two growing seasons, which consequently affected the yield. The effect of slags on common scab varied from year to year. In 2004, only few scab symptoms were observed due to a wet growing season. Therefore, it was not possible to determine the effect of slags on scab. In 2005, all slag amendments apart from the highest rate of converter slag (50 t/ha) increased the scab incidence, whereas in 2006, the slags did not significantly affect the scab.