Variations of lymphocyte subsets were followed longitudinally in 16 patients during an acute falciparum malaria attack. Before treatment, lymphocyte numbers were highly reduced, but the subset distribution was similar to that of healthy individuals. After parasite clearance, lymphocyte counts were normalized and the subset distribution was unchanged. This led to a normalization of all the absolute counts of lymphocyte subsets, except CD8+. The fast normalization of lymphocyte counts suggests that the initial decrease in lymphocyte numbers may reflect sequestration. Magnitude and kinetics of this variation were not related to parasite density or to severity of the attack. Activated T cells (CD3+HLA-DR+) were fewer in African than in European patients, suggesting the importance of the past exposure to malaria parasites in reallocation phenomena. These variations in lymphocyte numbers must be taken into account in the design and the analysis of cellular investigations in patients experiencing a falciparum malaria attack.