Cultivation parameters for the production of five lymphokines, granulocyte-macrophage colony stimulating factor (GM-CSF), interferon-gamma (IFN-gamma), interleukin 2 (IL-2), macrophage cytotoxicity factor (MCF), and macrophage migration inhibitory factor (MIF) from human spleen cells or peripheral blood lymphocytes were optimized. Cultivation was done in bioreactors containing up to 200 ml of medium, usually serum-free. The reactors were equipped with surface aeration facilities, stirrers and oxygen electrodes. Whereas stirring speed alone did not influence the yields of lymphokines, good aeration was especially beneficial for high IL-2 yields. However, all lymphokines were also produced under anaerobic conditions. The concentration of the mitogen concanavalin A was mainly critical for optimal IL-2 release. Optimal cell concentrations varied from 5 X 10(6)/ml (for GM-GSF and MCF) to 10 X 10(6)/ml (for IL-2 and IFN-gamma). It was possible to increase the yields of individual lymphokines 3 to 10-fold per batch of lymphocytes by a reinduction procedure which involved a change of medium and mitogen every 24 hrs. Reinduction was possible up to 4 times, especially when serum was present in the culture media.