Flow cytometer became one of the most pivotal and definitive techniques in the diagnosis and classification of mature B cell neoplasm (MBCN). Since flow cytometer exploits the laser and photomultiplier technology for reliable high quality result with extremely high sensitivity and specificity, we used these important specifications in this project to study the properties of B cells in the adult patients whose have initial diagnosis of (MBCN). This book discussed the diversity of the flow cytometer parameters (such as the percentage of positive cells, the mean fluorescence intensity and the positive peak width) which showed a remarkable role in the diagnosis of MBCN and in differentiation between CLL and NHL. The worth of the idea of this diversity of the parameters exhibited in the minimization of the markers number following into the minimization of panel cost without affecting the result. Also, using of CD20 & CD19 with their flow cytometric parameters and without the other scoring markers showed a significant role in differentiation between CLL and NHL. These ideas are appropriate for the used in laboratories of limited resources.