Immunotherapy of gynaecological cancer with tumour-infiltrating lymphocytes (TIL) or peripheral blood lymphocytes (PBL) has become a valid treatment modality with varying degrees of success in obtaining an antitumour response. TIL consist of lymphocytes, mainly T cells and minor populations of natural killer cells or B cells. Conventional cytogenetic studies of tumour cells from patients with breast and ovarian cancer have shown multiple chromosomal abnormalities including chromosomes 7 and 12. This study was designed to analyse the surface further, as well as investigate the intracellular, characteristics of TIL by multicolour flow cytometry and the cytogenetic features by fluorescence in situ hybridization. Tumour cell, peripheral blood and TIL samples from 25 patients (15 ovarian tumours, 8 breast cancers, 1 uterine sarcoma, 1 cervical carcinoma) were analysed for their phenotype, the expression of major cytokines [interleukin-2 (IL-2), IL-4 and interferon gamma (IFN gamma)], their proliferation rate, their cytotoxic ability and for the presence of numerical aberrations of chromosomes 7 and 12. All the tumour cells showed a high frequency of numerical aberration in chromosomes 7 and 12, especially trisomies or tetrasomies and combined aberrations. Trisomies of both chromosomes also occured at a low percentage in TIL and PBL. The phenotyping of TIL and PBL revealed rather similar subsets of lymphocytes. In both, T cells were the major population, with TIL containing a slightly increased CD4/CD8 ratio. The cytokine pattern showed a predominance of IL-4 production in TIL and of IFN gamma in PBL, indicating that, in TIL, cellular immunity is downregulated, whereas in PBL the cytotoxic immune response predominates. This is in accordance with the cytotoxic ability of TIL, which is weakened in comparison to PBL. Cellular characteristics revealed some disadvantages in the use of TIL for cancer treatment, explaining ineffective clinical results. The search for specific antitumour lymphocytes requires carefully designed experiments in order to define effective anticancer cells and thereby improve immunologically mediated tumour therapy.