Suspensions of fresh tumor-infiltrating lymphocytes (TIL) were prepared from 30 human breast ductal adenocarcinomas. To evaluate the phenotypic pattern of the isolated TIL, lymphocyte surface markers including CD19, CD3, CD4, CD8, CD16 and HLA-DR were examined by flow cytometry. Lymphocyte recovery ranged from 1.1% to 44%, independent of tumor size. TIL most often scored high for CD3+ with a varying number of CD4+ and CD8+ cells. Three samples out of 30 expressed up to 44% of CD19+ B cells, while CD3-CD16+ NK cells were rare. CD4 and CD8 expression was significantly different between the lymph node metastases group and the lymph node negative group (p < 0.01). 67% of the TIL with a CD4/CD8 ratio greater than 1 showed lymph node metastases. Furthermore, the CD4 expression of TIL and CD4/CD8 ratio correlated with tumor size (p < 0.01), but not with tumor differentiation and hormone receptor expression. Although there was considerable diversity of TIL among breast tumors, our data suggest that a high expression of CD4+ T cells may imply progression of the tumor, and an increased CD4/CD8 ratio of the TIL isolated from human breast adenocarcinoma may indicate development of metastases.