The project on control of seed potato quality was carried out in Nothern Ostrobothnia in 2003 2006. Effects of different cultivation techniques on seed potato quality were tested. The field experiments were carried out on seed potato farms and at MTT Ruukki research station. Haulm destruction reduced the vitality of seed potato. However, the effect on the yield on the following year was inconsistent. Preceding crops had little effect on the quality of seed crop. The results suggest that oat could be better and potato worse than barley as preceding crop for seed potato. The soil calcium content affected the quality and quantity of seed potato. Low calcium content in soil was followed by low calcium content in seed potato and it reduced yield in the following year. It was possible to increase the tuber calcium content during the growing season by applying calcium sulphate onto the hill after planting. However, ground limestone did not have the same effect. Washing of seed potatoes with ozonised water and a follow-up treatment with Agriclean delayed the growth and reduced the yield. They did not affect the disease resistance. None of the other treatments tested that combined washing and disinfection of the seed potatoes affected the disease resistance. However, some of them reduced the yield. Tuber dressing with Monceren or Rovral combined with Agriclean-treatment did reduce the amount of black scurf in the progeny tubers, but they did not affect the quantity of yield.