Measurable residual disease (MRD) is defined as a residual malignant population detectable by sensitive methods, such as four-color flow cytometry with a sensitivity of 10-4. MRD negativity was achieved with FCR treatment in 74.1% of patients and with BR treatment in 62.9%. The overall response rate (ORR) was the same in both groups – 97.8%. In the first-line treatment of refractory and resistant CLL, an ORR of 83% and a complete remission (CR) of 24% were achieved, with a median progression-free survival of 23 months. Complete remission lasts more than 3 months, while conditions such as a normal blood cell count and no lymphadenopathy are met. MRD is used as a treatment target and to monitor response to therapy. The results show that MRD negativity is associated with a better outcome of CLL treatment.