Plasma fibrinogen levels were measured, by a clotweight method, in 25 patients with homozygous sickle cell disease (HbSS) during the steady state and in 36 age matched non-sicklers. Mean fibrinogen levels in the sicklers was 5.3 +/- 2.0 g/l (range 3.0-11.5 g/l) compared with 3.1 +/- 1.0 (range 2.0-5.5 g/l) for non-sicklers (p less than 0.001). There was no significant sex difference between males and females in either group. We suggest the raised fibrinogen seen in SCD may be an added factor in the severity of vascular occlusion during SCD crisis.