Splenic reticuloendothelial function, as determined by pitted red cell counts in 114 pediatric patients with sickle cell disease, was evaluated. Patients with homozygous sickle cell disease (HbSS) had a mean pit count of 11.8 +/- 7.0% and the count increased with age. Sickle cell hemoglobin C disease (HbSC) patients had a mean pit count of 4.9 +/- 9.1%, the count being unaffected by age. One patient with HbS-beta thalassemia had a count of 12%, while eight patients with HbS-beta + thalassemia had a mean count of 0.4 +/- 0.3%. There was one patient each with HbSS-alpha thalassemia, HbS-O Arab, and HbS-Lepore, and the pit counts were 4.9, 31.4, and 0.4%, respectively. In both HbSS and HbSC patients, the pit count was significantly lower in patients who had palpable spleens. The pit count may be used as a predictor of disease severity in the sickle cell disorders.