Employing a multicolour flow cytometry assay, 133 B-chronic lymphocytic leukaemia (B-CLL) cases were analysed for surface expression of CD38. Based on a cut-off value of 20%, CLL patients were categorised into a CD38-positive (> or = 20%, n = 56) and a CD38-negative subgroup (< 20%, n = 77) and separately analysed for clinical and laboratory parameters. Patients in the CD38-positive cohort were characterised by an unfavourable clinical course with a more advanced disease stage, poor responsiveness to chemotherapy, short time to initiation of first treatment and shorter survival. In contrast, the CD38- negative group required minimal or no treatment, remained treatment-free for a longer time period and had prolonged survival (P < 0.05). CD38 expression was a robust marker in the majority of patients in that it was stable over time and not significantly influenced by chemotherapy. In conclusion, our data confirm recent studies suggesting a role of CD38 as a predictor of clinical outcome in patients with B-CLL.