The French Groupe d'Etude Immunologique des Leucémies (GEIL), now in its fifth year of existence, has collected extensive immunological information on more than 1,000 leukemia patients. The rationale of such multicentric group is to improve immuno-phenotyping and investigate rare phenotypes, with relevance to the clinical outcome of the patients. These aims are described and exemplified through 3 of the first studies performed.