The prevailing dogma of the cell cycle posits that a mitogenic signal is required at the end of each mitosis for cells to progress through the next G1. This textbook model is based mostly on experiments with fibroblast cultures. Burnet’s clonal selection theory states that selected B and T cells expand rapidly to initiate immune response. To achieve this, it is plausible that lymphocytes do not follow the canonical rules of cell cycle progression. One such cell cycle anomaly lymphocytes demonstrate is non-dependency on mitogenic signals during proliferative phases. Such modified cell cycle regulation mechanisms can play a critical role in the outcome of immune response to the invading antigens. Similarly, such responses against self-antigens can lead to autoimmunity, and dysregulation of this process can cause lymphoma and leukemias. Here, we provide a method to explore mitogen-independent proliferation properties of murine splenic B cells. This protocol can be further combined with other molecular techniques to obtain deeper molecular mechanisms of cell cycle regulation in lymphocytes.