Deletions on the long arm of chromosome 6 are frequently found in acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphomas (NHL). We have used polymerase chain reaction analysis to study loss of heterozygosity of 16 microsatellite markers on chromosome 6 in 74 ALL and 54 NHL patients. Our results show that deletions of 6q in ALL are more frequent than what has been reported in previous studies, occurring in at least 32% of the patients. The corresponding figure for NHL patients is 7%. Our results define a region of minimal deletion in ALL of less than 500 kb between markers D6S1709 and D6S434. The common region of deletion in NHL is located telomeric of this region. Thus, two different tumor suppressor genes on chromosome 6q seem to be relevant for the development of lymphoid malignancies.