The in vitro lifetime of 100 salivary gland pleomorphic adenomas was investigated. On the average, they had a limited lifetime of 3.7 passages. In 86 cases, the tumors were successfully karyotyped, resulting in three major cytogenetic subgroups characterized by either an apparently normal karyotype or by rearrangements of 8q12 or 12q13-15. There was no significant difference between the in vitro lifetime of the tumors with a normal or with an aberrant karyotype. The three adenomas with the longest lifetime were characterized by an unbalanced karyotype. One of them had a deleted chromosome 6, which has also been described in malignant tumors. An increased in vitro lifetime may thus correspond to early steps of malignant transformation in vivo and can be caused by additional unbalanced chromosome aberrations. In the future, long-term cultivation can be helpful in defining chromosomal regions involved in this process.