RÉSUMÉ
INTRODUCTION: A significant peripheral blood plasmacytosis is a rare finding associated with viral infections. We reported five consecutive cases of dengue virus infection, with circulating plasma cells. CASE REPORTS: Three women and two men, aged 26 to 75 years, had returned from French West Indies less than one week before the onset of the symptoms (mean: 2.5 days). The transient blood plasmacytosis was variable in intensity (0.1 to 0.8 G/L) with a maximal level between the fourth and the seventh day following the onset of the symptoms, and was associated in four patients, with activated lymphocytes and lympho-plasma cells. CONCLUSION: Reactive plasmacytosis during dengue fever is common and probably underestimated because it is transient and only identified by careful microscopic examination of a blood smear. Plasmacytosis could be explained by the intensity of the immunological response and the production of large amount of interleukins.