Characterization of clonal cytogenetic changes in a variety of human neoplasms has provided valuable information regarding both etiology and progression of these cancers. The problems with the cytogenetic study of breast cancer are the difficulty in initiating short term culture and their complex chromosomal changes. The aim of this study was to find out the appropriate culture conditions and to invastigate the cytogenetic characteristics of primary breast cancer. Different growth media and procedures for tissue disaggregation and clulturing were tested with regard to cell attachment, the type of cells in the outgrowth, and the emergence of cytogenetically abnormal clones. Specimens from 20 primary breast infiltrating ductal carcinomas with or without axillary lymph nodes metastasis, T2 were used in this study. We found out that optimal tissue disaggregation was obtained by combined mechanical and enzymatic treatment of the tumor samples. Use of the plastic flasks coated with Vitrogen 100 and the serum free growth medium containing epidermal growth factor resulted in the best outgrowth of epithelial cells and also simultaneously in the least outgrowth of fibroblast. Chromosomal abnormalities were found in all 20 tumors. The changes were clonal in 10 tumors(50%), and nonclonal aberrations were more common. Karyotypic analyses of first or second passage cultures yielded predominantly diploid cells. Among the clonal aberrations, clones with 15q deletion[ql3-q15, ql2-q15, q?) were observed in 4 cases. In addition, there were two clones involving the chromosome 1, one was a Ip31 deletion and the other was a Iq21 deletion. But it has been well known that the most common cytogenetic abnormalities in caucasian breast cancer affect chromosome 1.