Treatment of the anaemia of renal disease with recombinant human erythropoietin results in an improvement of haemostasis and an increased risk of thrombovascular accidents. In this prospective, placebo-controlled, double-blind, and cross-over study, the effects of low-dose acetylsalicylic acid (30 mg daily) on thrombotic and bleeding events during the initial period of treatment with erythropoietin in anaemic haemodialysis patients without previous thrombovascular accidents or known increased risk for thrombosis were investigated. During correction of the haematocrit and the first 3 months thereafter, group A (n = 68) received placebo and group B (n = 69) 30 mg acetylsalicylic acid daily. Cross-over took place after the 3rd month of a stable haematocrit. The study ended 3 months later. Target haematocrit (30-35%) was reached in 12.4 +/- 8 weeks (M +/- SD). In group A the bleeding time was 382 +/- 285 s, decreasing to 282 +/- 208 before cross-over (P < 0.01), and increasing to 395 +/- 271 (P < 0.05) thereafter. In group B the bleeding time was 390 +/- 381 s, 406 +/- 267 (NS), and 285 +/- 238 (P < 0.05) respectively. Twenty-two thrombovascular accidents were seen (16%, 13 during acetylsalicylic acid and 9 during placebo, NS), including 17 fistula thromboses. The incidence of bleeding events was not significantly different between regimens. In conclusion, erythropoietin treatment resulted in a reduction of the bleeding time. When 30 mg acetylsalicylic acid was taken during the treatment, the bleeding time did not decrease.(ABSTRACT TRUNCATED AT 250 WORDS)