Veno-occlusive disease (VOD) is a major cause of toxic death after autologous bone marrow transplantation (ABMT). We studied the potential role of continuous administration of low-dose heparin for VOD prevention in 234 consecutive patients who underwent ABMT in our institution. The population consisted of 98 patients autografted before October 1984 who did not receive heparin, and a series of 136 patients autografted from October 1984 to March 1989 containing 98 patients included in a randomized trial comparing heparin administration (n = 52) vs no heparin (n = 46), and an additional group of 38 patients who received non-randomized heparin in view of high-risk criteria to develop VOD (n = 31) or other reasons unrelated to VOD (n = 7). Overall, 90 patients (38%) received heparin and 144 (62%) did not. The global incidence of VOD was 13/234 (5-5%). Heparin did not reduce the risk of VOD in all subgroups studied. In particular, in the randomized trial, the incidence of VOD was 2.2% in the group without heparin vs 7-7% in the group receiving heparin. We analyzed in depth the 13 patients who developed VOD and we compared them to a control group of 13 patients pair-matched for age, sex, diagnosis and preparative regimen, who did not develop VOD. We found that abnormal LFT before ABMT predisposed patients to VOD; refractoriness to platelet transfusion was observed in 85% of the patients in the VOD group vs 15% in the control group (p less than 0.05). VOD patients had an increased requirement for red cells and platelet transfusions, a lower recovery (R less than 25%) after the second and third platelet transfusion, and shorter intervals separating the first four platelet transfusions. Further, the platelet reconstitution after ABMT in the VOD group was slower in comparison to the control group (p less than 0.01). Again, in this pair-matched analysis continuous infusion of low-dose heparin did not prevent VOD.