In order to examine the effects of platelet-activating factor (PAF) in complicated Plasmodium falciparum infections, plasma concentrations of lyso-PAF, stable metabolite and principal precursor of PAF, were measured in 25 Vietnamese adults with severe malaria. The concentration of PAF in the cerebrospinal fluid (CSF) was determined in a sub-group of 23 comatose patients and, together with that of lyso-PAF, in the plasma of 20 patients on recovery of consciousness. The concentration of lyso-PAF in the plasma was depressed on admission to hospital (median [range]; 21 [8-143] vs. 293 [215-410] ng/ml in 10 controls; P < 0.001). There was, however, no change in plasma activity of acetylhydrolase which converts PAF to lyso-PAF (P > 0.01 vs. controls) while simultaneous reduction in the concentration of lipoproteins associated with lyso-PAF were less than those of lyso-PAF per se in the plasma. The plasma concentration of lyso-PAF on admission was associated with parasitaemia and the concentration of serum triglycerides (rs = -0.42, P = 0.04 in each case), the latter being consistent with hepatic effects of PAF reported in previous studies. CSF concentrations of PAF on admission were low (2.3 [0.5-7.7] vs. 0.9 [0-2.5] ng/ml after recovery, P < 0.01) compared with values reported previously in bacterial meningitis. Plasma concentrations of lyso-PAF after recovery lay between admission and control values. While increased availability of PAF may reflect parasite burden and may modulate liver-mediated metabolic disturbances such as hypoglycaemia and lactic acidosis, the role of PAF in cerebral malaria is uncertain.