Daily serum samples collected during 6 autologous and 13 allogeneic BMT were assayed retrospectively for tumour necrosis factor-alpha (TNF), interleukin-6 (IL-6) and C-reactive protein (CRP). In addition, for 6 allogeneic transplant patients soluble TNF receptor (sTNFR) levels were determined. IL-6 levels were regularly raised during febrile episodes and closely mirrored changes in serum CRP but were not predictive for non-infectious major transplant-related complications (TRC). Levels of TNF showed no such close association with infection and in contrast to previously reported data for allogeneic transplants having TRC, TNF levels were consistently detectable in only 3 of 9 patients. Pre-transplant levels were not predictive for the development of TRC and no profile was recognized to be specific for a particular complication. In transplants with only minor complications TNF levels remained consistently undetectable. sTNFR levels increased in a more stable manner in association with TRC, suggesting that they may be a more suitable marker to monitor major TRC.