Apoptotic cell death plays a central role in the pathogenesis and disease progression of cancer as well as in the response to treatment. In the present work we investigated the association between the presence of apoptotic peripheral blood cells in breast and ovarian cancer progression. Apoptosis was analysed in blood cells of breast (n=82) and ovarian cancer patients (n=79). Blood samples from age matched healthy women served as control (n=70). The apoptotic peripheral blood cells were detected by agarose gel electrophoresis. The apoptotic cells were identified in 83% (68/82) of the breast cancers and in 65% of ovarian cancer patients (51/79). The number of positive samples was significantly higher among cancer samples than among control samples (p<0.05). Additionally, there were significant differences (p<0.05) in the presence of apoptosis between subgroups assigned to histological stage. The high frequency of apoptotic peripheral blood cells in breast and ovarian tumours suggests a potential role of apoptosis in cancer appearance and/or progression.