Peripheral blood lymphocytes from five chronic lymphocytic leukemia (CLL) patients were cultured with PHA for 3-6 days. Chromosomal analysis with G-banding showed 25% of the diploid metaphases were pseudodiploid as a result of either a chromosomal deletion or a translocation. Abnormal clones with 18p- were seen in two patients, and two other patients had 18p- metaphases, but with other inconsistent abnormal chromosomes. None of the patients had trisomy 12, which has been thought by some to carry a poor prognosis. Although no conclusion can be reached regarding the significance of the chromosomal abnormalities in CLL, the type of chromosomal abnormalities in these patients suggests that they are the result of chromosomal breakage and abnormal repair.