The malignant B cells of patients with chronic lymphocytic leukaemia (CLL) constitutively express interleukin 8 (IL-8) and IL-8 receptors. Ex vivo culture with exogenous IL-8 enhances IL-8 expression and prolongs leukaemia cell survival, partly through increased bcl-2 expression. IL-8 may function as an autocrine growth and apoptosis resistance factor in CLL. Therefore, we evaluated the prognostic relevance of plasma IL-8 levels in 151 CLL patients [median age 61 years (range, 32-84 years), median plasma IL-8 level 18.9 pg/ml (9.1-89.1 pg/ml)]. All Rai stages were represented; advanced stage was associated with significantly higher plasma IL-8 levels (P < 0.0001, Kruskal-Wallis). Also, plasma IL-8 level was correlated with serum beta2-microglobulin (beta2-M) (R = 0.24, P = 0.0081), haemoglobin (R = -0.39, P < 0.0001) and platelet count (R = -0.23, P = 0.0049) by Spearman's rank correlation. Univariate analysis using Cox proportional hazards models identified elevated IL-8 and beta2-M as significant prognostic factors with relative risks of 7.43 (P = 9.1 x 10(-9)) and 16.40 (P = 5.9 x 10(-10)) respectively. High levels of IL-8 were associated with shorter survival independent of beta2-M level. Using recursive-partitioning procedures, an IL-8 cut-off point of 26.2 pg/ml segregated a group of CLL patients with significantly shorter survival (median 9.3 months) (P < 0.0001). In conclusion, plasma IL-8 level in CLL patients correlates with other prognostic factors, such as Rai stage and beta2-M, and is associated with increased risk of death in CLL patients. The role of IL-8 inhibitors in the treatment of patients with CLL should be explored.