We investigated the cytokine profile and peak levels of interleukin (IL) -6, IL-8, IL-10 and tumour necrosis factor (TNF) -alpha levels in 42 patients after allogeneic bone marrow transplantation (BMT). Eleven of them developed veno-occlusive disease (VOD) of the liver. Fourteen patients had moderate-to-severe acute graft-versus-host disease (aGvHD), 10 isolated bacteraemia and 7 had no major complication. Those who developed severe VOD (n=6) showed a short, very high IL-8 peak (median: 6632 pg/ml, range: 5546-10,000 vs. 280 pg/ml, 0-2042 in controls, p<0.01) 1-4 d after diagnosis of the liver disease. Five of these patients had high peak levels of IL-6. Five patients with mild VOD showed a lower increase in the cytokines tested. Bilirubin levels, at day of IL-8 peak, did not differ statistically between mild and severe VOD. The highest levels of IL-10 were found in those with aGvHD. IL-8 levels were also increased, but not to the same extent as in patients with severe VOD (p=0.01 vs. VOD). In patients with bacteraemia, very high levels of IL-6 were seen. In patients without major complications, the levels of cytokines were low. In conclusion, high levels of IL-8 occurred in severe VOD of the liver, which may be of value to determine prognosis.