Within the pathology of human reproduction, genetic abnormalities play an important role in spontaneous abortions. This paper describes the morphologic, karyotypic features of a consecutive series of singleton spontaneous abortions collected as part of this study and also reports the application of the alkaline comet assay to assess levels of DNA damage in 31 couples comprised of 13 control couples and a patient group of 18 couples with a history of more than one fetal loss. For the cytogenetic analyses, the conventional lymphocyte culture method was applied to all subjects. In this analysis, two women with habitual abortion were determined to carry balanced chromosomal translocation. The alkaline comet assay (single cell gel electrophoresis technique) was applied also to lymphocytes. The comparison of the results of alkaline comet assay in patient and control individuals showed a significant difference in the number of damaged cells. The cells were evaluated according to their grades of damage as: normal (undamaged-no migration), limited migration, (at low damage level) and extensive migration (comet imaged cells-with increasing numbers of breaks, DNA pieces migrate freely into the tail forming a comet image). The frequency of limited migrated and extensive migrated cells in the women in the patient group were higher than in the women in the control group (p < 0.001). However, all above parameters were equal for husbands in both the control and patient group (p > 0.05). (C) 1998 Elsevier Science B.V. All rights reserved.