Approaches to modify disease resistance or susceptibility by transgenic means will be a major asset to animal welfare as well as to the economics of animal production. Candidates for gene transfer experiments include all genes known to influence non-specific and specific host defence mechanisms against infectious pathogens. Additional strategies such as "intracellular immunization", "genetic and congenital immunization", antisense RNA approaches and targeted disruption of disease susceptibility genes promise to gain importance in conferring increased disease resistance. The cytokine network regulates cellular viability, growth and differentiation in physiological and pathophysiological states. Detailed understanding of cytokine signal transduction pathways and transcriptional activators will provide not only new target molecules for modulating the immune response but will also facilitate the elucidation of host-pathogen interactions.