The primary culture bone marrow (PCBM) cells are often used in different cytological investigations. Here we study the behavior of porcine unstimulated PCBM cells during the cultivation. DNA cytophotometry analyses revealed that immature white blood cells (WBC) such as lymphoblasts, monoblasts and myeloid cells during cultivation process reduced the DNA content in the nuclei. This resulted in displacement of the DNA histogram to the left and increased the content of diploid nuclei. This is a result of cells unblocking which are in G2 cell cycle phase. We also observed diploid pathological cells with accessory or fragmentized nuclei. However, the data with erythroid cells (EC) somehow demonstrate the opposite tendency. During the late stage of cultivation, the number of immature EC with the tetraploid DNA is increased.