Cytogenetic analysis of peripheral blood lymphocytes of 19 colorectal cancer patients was carried out in short term blood cultures (T-cells) as well as in Epstein-Barr virus transformed B-cell lymphoblastoid cell lines. One hundred Giemsa-banded metaphases from the T lymphocytes and 50 metaphases from the B lymphocytes of each patient were evaluated for cytogenetic abnormalities. Clonality was not observed in every paired sample. Structural and/or numerical aberrations were most frequent in chromosomes #1, #2, #5, #7, #9, #12, #14, #17, #18 and #21. Aberrations among these chromosomes could be observed individually in either of the cultures, which proves that the analysis of both cultures (T and B cells) is complementary to each other. In some cases involving multiple primary cancers it was interesting that the specific chromosomal change, crucial for a particular malignancy, was identified only in the lymphoblastoid cell line analysis. This supports the notion that B-cell analysis can serve as a useful adjunct to the study of short-term blood cultures and also poses a question as to whether the specific chromosomal changes observed in the analysis are confined to the B-cell lineage.