High-dose dexamethasone was compared with placebo in a double-blind trial involving 100 comatose patients with strictly defined cerebral malaria. The two treatment groups, whose members were six to 70 years old, proved comparable on admission. There were eight deaths in the dexamethasone group and nine in the placebo group (no significant difference; P = 0.8); at post-mortem examination the brain showed features diagnostic of cerebral malaria in all but one patient who died. Dexamethasone prolonged coma among the survivors: the interval between the start of treatment and the full recovery of consciousness was 63.2 +/- 5.9 hours (mean +/- S.E.M.) in the dexamethasone group, as compared with 47.4 +/- 3.2 hours in the placebo group (P = 0.02). Complications, including pneumonia and gastrointestinal bleeding, occurred in 26 patients given dexamethasone and 11 given placebo (P = 0.004). Only five patients had neurologic sequelae. Results were similar in a subgroup of 28 children six to 14 years old. Dexamethasone is deleterious in cerebral malaria and should no longer be used.