The authors evaluated retrospectively a group of 12 patients with B-chronic lymphatic leukaemia to whom fludarabine was administered. All patients had been treated in the past by combined chemotherapy (1-4 regimes, median 3). Fludarabine was administered in amounts of 30 mg/m2/day for 5 days to 4 patients and for 3 days to patients. The median of the number of administered cycles was 3. Only two patients achieved partial remission of the disease, the reminder did not respond to therapy. All patients had complications which very probably were associated with the administered treatment. A total of 21 episodes were recorded in the course of 36 cycles, 1 complication per 1.7 cycles. The most frequent complications were infections, a total of 14 episodes, incl. 3 invasive aspergilloses. Infections were more frequent in patients with a 5-day cycle, the majority was recorded after the first two cycles. Eight patients (67%) died from complications which developed in the course of treatment or after its termination. The author's experience with the administration of fludarabine in intensively pretreated patients with advanced forms of B-chronic lymphatic leukaemia indicates that this treatment is associated with a large number of serious complications, which are not compensated by a corresponding therapeutic effect.