Our development of genetic immunization (unfortunately named 'DNA'-immunization at times) seems to have great promise as a vaccine delivery system. However, one is still left with the often formidable problem of discovering what gene of the pathogen to include in the genetic immunization vector. The is particularly a problem with pathogens with large genomes such as bacteria and parasites. We have developed a potential solution to this problem termed 'expression library immunization'. It involves using expression libraries in genetic immunization vectors to basically strip down the genome into protective genes. It may offer a systematic, unbiased approach to discover vaccine candidates.