Plasma levels of GM‐CSF, IL‐3, IL‐6 and IL‐1(α,β) were investigated in steady‐state sickle cell patients. We find that SS patients with low levels of HbF (< 9% [LFSS]) are characterized by elevated plasma GM‐CSF, whereas in patients with high levels of HbF (HFSS), GM‐CSF is not detectable. In contrast, HFSS patients exhibited increased plasma IL‐3 (m = 84.8 ± 57pg/ml), whereas LFSS patients had lower or no detectable plasma IL‐3. IL‐1(α,β) and IL‐6 were also detected in plasma from some SS patients, but there was no correlation with HbF levels. Normal controls tested negative for all cytokines, except for one individual positive for IL‐3. These results are compatible with a model in which the level of haemopoietic stress determines the level of participation of GM‐CSF or IL‐3 in the regulation of SS circulating BFU‐E.