The study by Sutton et al. in this issue of GASTROEN-TEROLOGY represents application of new technologies to an old question. 1 The new technology is a technically sophisticated technique termed ‘‘representational difference analysis.’’This technique involves a combination of subtractive hybridization plus polymerase chain reaction amplification to enrich DNA sequences that are present in one sample of DNA but not another. 2

Only a portion or representation of the total DNA in a sample is used, thus the name. Enrichment of nonshared sequences of greater than 1010 can be achieved, thus this technique can detect a difference of a single DNA sequence between 2 samples. The old question being asked is whether this technique might allow identification of foreign, ie, microbial, genes in the lesions of Crohn’s disease. To this end, lamina propria mononuclear cells were isolated from inflamed and noninflamed areas of colon from a patient with Crohn’s disease. Indeed, this technique did identify a sequence of microbial DNA,