['The ability for engulfment of pathogens and inert particles is the key hallmark of the phagocytic cells. Phagocytes play a significant role in the modulation of local or extended inflammation. Since fever activates a number of factors linked with the immune response it was the goal of this study to examine the in vitro effect of hyperthermia on the phagocytic capacity, the number of phagocytic cells and the viability of human peripheral blood mononuclear cells (PBMC) at 37 and 40°C.', 'PBMC were incubated with 0.8 μm polysterene latex beads, for 2 hours at 37 and 40°C. The number of phagocytic cells, and that of latex particles internalized by each individual cell was counted with a light microscope. In addition, the percentage of viable cells and the number of active metabolic cells was evaluated.', 'A temperature of 40°C significantly increased the number of phagocytic cells and the phagocytic index by 41 and 37% respectively, as compared to cells incubated at 37°C. While the number of vital cells (trypan blue test) did not differ statistically at both temperatures, the number of active metabolic cells (XTT test) after 2 h of incubation at 40°C was 17% higher as compared with that at 37°C. However, the number of active metabolic cells after 24 h of incubation at 40°C was 51% lower compared with cells incubated at 37°C.'] Does high temperature affect the phagocytic activity of human peripheral blood mononuclear cells?