Cytokines are essential mediators in infection and inflammation. Almost all cytokines have not only positive but also noxious effects: the proinflammatory cytokines released during severe infections in high concentrations lead to organ damage and death. The antagonistic anti-inflammatory cytokines inhibit the defense against infections. Immunotherapy through modulation of the cytokine response may aim at inhibition of the proinflammatory and reinforcement of the anti-inflammatory cytokine response, so as to limit the damage of inflammation. In patients with sepsis this has so far been little successful, probably owing to the multiple effects of the cytokines. Inhibition of proinflammatory cytokines was successful, on the other hand, in patients with rheumatoid arthritis or Crohn's disease. Another possibility is to aim, on the contrary, at reinforcement of the proinflammatory and inhibition of the anti-inflammatory cytokine response, to strengthen the resistance of the host. This has given favourable results in a limited number of infections.