Twenty-three consecutive oncology patients (mean age, 30; range, 19-34 years) were recruited to assess the DNA integrity and mitochondrial function of spermatozoa of patients prior to treatment. Fourteen men (mean age, 32; range, 22-60 years) were recruited as controls. For studies of sperm chromatin condensation, neat frozen semen samples were stained with the DNA fluorescent probe propidium iodide and for assessment of mitochondrial function with the fluorescent dye rhodamine-123. Samples were analyzed on a FAC Star Plus (Becton Dickinson) flow cytometer. To study DNA integrity, frozen semen samples were evaluated using the single-cell gel electrophoresis (Comet) assay. Intact and damaged DNA were quantified using epifluorescence microscopy and image analysis. The results demonstrated a significant reduction (p < .05) in the distributions of spermatozoa with condensed chromatin in the spermatozoa of men with cancer. There was a significant difference in DNA integrity in patients with neoplastic disease. The median percentage head DNA intact was 44.5% in cancer cases versus 84.5% intact in controls (p < .001) (median values). There were no differences detected in mitochondrial DNA fluorescence between study cases and controls (rhodamine-123 uptake: 48.7% vs 56% [median values]). In this study, patients with neoplastic disease had decreased DNA integrity and chromatin condensation in their spermatozoa compared with controls. No difference was seen for mitochondrial activity. [ABSTRACT FROM AUTHOR]