Erythrocyte survival was studied in 17 Thai patients (10 males, 7 females; aged 13-57 years) with severe falciparum malaria. To ensure radioisotopic labelling of cells before bone marrow recovery and survival analysis under near-steady state conditions, 51Cr labelling of autologous erythrocytes was performed at the time of admission (0 h) and calculation of mean cell lifespan (MCL) was based on semilogarithmic plots of corrected counts from 60 h onwards. Five patients received blood transfusions, all within 48 h of admission. The overall mean (+/- S.D.) MCL was short (44.1 +/- 21.7 days). Nontransfused patients had similar MCL values (43.6 +/- 20.4) to those of transfused patients (45.5 +/- 27.3 days, p greater than 0.8). Patients with and without palpable splenomegaly had MCL values which were not significantly different (54.1 +/- 28.8 vs. 37.2 +/- 12.3 days respectively, p greater than 0.1). There was no association between admission haematocrit or peripheral parasitaemia and MCL (p greater than 0.2 in each case), but there was an inverse correlation between total serum bilirubin and MCL (r = -0.49, p less than 0.025). There is accelerated destruction of non-parasitised erythrocytes in severe malaria resulting in a mean MCL that is half that found previously in healthy Thai volunteers (89.6 +/- 13.1 days, p less than 0.001) and significantly shorter than that reported previously in Thai patients with uncomplicated P. falciparum infections studied after parasite clearance (56.8 +/- 10.2 days, p less than 0.05).