A clinicopathological study was performed on 115 patients (56 males, 59 females; median age 48 yr) with chronic myeloid leukaemia (CML) to reveal initial clinical, but particularly histomorphological features of predictive value for survival. All patients had a trephine biopsy of the bone marrow and entered this study without prior selection. Overall survival was 36 +/- 27 months. In addition to multiple interactions between various disease features, multivariate regression analysis showed that of the clinical parameters age, liver size and level of LDH were primarily and most closely associated with prognosis. Of the histomorphological variables, megakaryocytes greater than 60 mm-2 bone marrow area and fibrosis displayed an unfavourable impact on survival on univariate calculation. On multivariate analysis, however, only pseudo-Gaucher cells remained significant, i.e. exerted an independent and favourable influence on prognosis. Histological features of predictive value were reviewed together with the different categories of a histopathological classification proposed for chronic myeloproliferative diseases by Georgii and co-workers.