The issues discussed in the text below refer to changes in the settlement of the Tarnobrzeg – Koprzywnica region from the fourth period of the Bronze Age to the Early Iron Age. During this period, the Tarnobrzeg Lusatian culture was being developed here and as for HaC and D phases the Pomeranian culture also appeared. The article draws attention to the difference considering the population of the Tarnobrzeg Lusatian culture in I and III phase of its development. It mainly emphasises the issue of rapid population growth in the third phase. It seems that it cannot only be explained by a gradual process of increasing population. This growth can be partially explained by means of the emergence of the Pomeranian culture. However, regarding the areas of the east Vistula river the flow of mentioned population was small and it could not provide the expected results. What is more, with regard to the Połaniec Basin this culture did not appear in general. Only as far as the Sandomierz Upland is concerned, the impact of the mentioned culture was marked more intensely, but it seems that it was a place where a combination of the two groups appeared and the formation of the mixed Pomeranian – Lusatian group took place. It forces us to trace also other directions of people influx which could explain the occurring differences.