The chromosomal abnormalities of squamous cell carcinoma developed in the human lower lip were analyzed with cancer cells of 3 weeks old primary culture and propagated cells after continuous culture for 8 months in vitro. Hypodiploid pattern cells appeared on primary culture in general. In contrast hypotriploid, hypotetraploid and hypertetraploid pattern cells appeared in continous culture from passage 2 to passage 5. The characteristic structural abnormality was del 6(q21-pter) in primary culture. In addition, unidentified metacentric chromosome and dicentric chromosome were also found in minority. New abnormalities such as t(6 ; 11), t(9 ; 15), t(11 ; 14), t(8 ; X) and iso (15q) were found in continous culture but del 6(q21-pter) which was prominent at primary culture was decreased. These abnormalities increased in accordance with increase of culture time, which suggests the cancer instability is high in accordance with culture time and variety of genetic alteration could also occur after long term culture in vitro.