The pathogenesis associated with Dengue haemorrhagic fever, has yet to be fully elucidated, with no definitive in vivo evidence. The exceptional epidemiological circumstances in Cuba allow the evaluation of different mediators in a well‐defined situation. In the present study, we describe the determination of levels of IL‐12, IL‐10 and RANTES in the sera of Cuban patients hospitalised with Dengue fever or Dengue haemorrhagic fever. The results showed that levels of serum IL‐10 were higher in patients than controls, and those patients with secondary infections had consistently higher levels. All the Dengue haemorrhagic fever patients had increased levels of IL‐10. In contrast, levels of IL‐12 did not differ between patients and controls. Finally, RANTES serum levels detected in patients were lower than those observed in the controls. The association of increased levels of IL‐10 in Dengue patients with a sequential infection suggests a possible role of this cytokine in the pathogenesis of Dengue disease. J. Med. Virol. 73:230–234, 2004. © 2004 Wiley‐Liss, Inc.