Among other patient and disease characteristics, different morphological lymphocyte subtypes were analysed in 146 patients with chronic lymphocytic leukaemia (CLL) to establish their clinical significance and prognostic value. The univariate analysis selected, among other well-known variables, the following lymphocyte subtypes as significant in prognosis: prolymphocytes, granulated lymphocytes, cleaved lymphocytes and small-size lymphocytes. The presence of prolymphocytes and cleaved lymphocytes was correlated with a poor prognosis, whereas granular lymphocytes and small-size lymphocytes were related to a good prognosis. A multivariate regression analysis showed that, besides clinical stages, haemoglobin level, WBC count, age, percentage of bone marrow erythroid cells, and sex, only prolymphocytes had independent prognostic significance. Prolymphocyte percentage correlated positively with characteristics expressing tumour mass such as WBC count, blood absolute lymphocyte count, serum lactate dehydrogenase level, number of enlarged lymph nodes, splenomegaly, and a high number of lymphocytes in bone marrow aspirate. Finally, a prolymphocyte threshold of 5 x 10(9)/l was found to be useful not only to separate two different groups of patients in the whole series but also in Rai's stages II and III + IV, and in Binet's stages A and C.