The importance of cell morphology with respect to the presence or absence of nuclear clefts (NC) in peripheral blood lymphocytes has been investigated in 86 previously untreated chronic lymphocytic leukemia (CLL) patients. Cleaved cells were considered to be present in significant numbers when they exceeded 5% of the peripheral blood lymphocytes. On this basis patients could be divided into two morphological groups. Age, sex and distribution of stages, as well as mode of clinical presentation were alike in the two groups of patients. In contrast, lymph node involvement was more frequently encountered in patients with NC greater than 5% (p less than 0.01). Both survival and treatment-free period probabilities were not statistically correlated to the quantitative changes in the percent value of NC. We further confirm that Binet's clinical staging is a significant predictor of survival irrespective of NC.