There are various indices used to assess the effect of thermal processing conditions on nutritional value, however, there are only little analyses the results of which refer to the content of reactive lysine (with a free ε-amine group). The following was determined in seeds of 3 soybean types (Augusta, Aldana, and Progres): content of basic components, amino acids, and reactive lysine; composition of fatty acids and mineral components; and ureasic activity. The seeds were autoclaved at a temperature of 121 ºC during 10, 20, 30, and 2×30 minute periods and the content of reactive lysine was determined therein. After the seeds of the Progres variety have been exposed to the processing conditions for 20 minutes, statistically significant losses of reactive lysine were found in those seeds, whereas in the seeds of the Augusta and Aldana varieties showed such losses after having been autoclaved for 30 minutes. It was found that the autoclaving process of soybean seeds resulted in a significant decrease in the ureasic activity.