The production of potato starch leads to large amount of separate cellular liquid. So far industries haven’t had use for this potato juice, and it has been distributed back to fields. This causes unnec-essary expenses for industries as well as raises the risk of nutrients leaching. These factors have raised the interest in developing processes for further processing of the cellular liquid. The main interest of industries is still potato starch, which is why they are interested in what affects the nitro-gen and protein content of starchy potatoes and what is their relationship to starch content. This study was done in unison with Perunantutkimuslaitos (Petla) during the starch potato variety test in summer of 2016. In this study the effects of four cultivational factors (site, cultivar, nitrogen fertilization level and time of harvest) were examined via the changes in nitrogen and protein levels in tubers. The weather factors were considered from the data collected from the nearest measure-ment location of the Finnish Meteorological Institute. The goal of the study was to find out what are the factors that have the biggest effect on the changes in nitrogen and protein contents of starch potato variants. Cultivars were found to have the biggest effect, but the site as well as sowing time and weather conditions had an effect as well. Correlation between starch and nitrogen content was not observed. In addition, the goal was to determine the ideal combination of cultivational factors for optimal starch, nitrogen and protein yield. Early variants do have more secure production of yield, since late variants are easier affected from different growing conditions. Raising the level of fertilization to 100 kg/ha was the optimum based on the results of this study, but only if time of harvesting was opti-mized as well.