The purpose of this study was to describe the quantity and distribution of deoxyribonucleic acid (DNA) in oocytes that did not fertilize or did fertilize and failed to cleave, from patients who underwent in vitro fertilization. Patients were selected with at least one cleaving egg, so that the sperm population was known to be fertile, and failure of fertilization or cleavage in the remaining oocytes could be attributed to nonspermatozoan factors. The noncleaving oocytes were classified into five categories, the majority of which (71%) lacked a polar body and any morphologically identifiable nucleus or germinal vesicle. Three general defects were found: (1) failure to replicate the DNA properly; (2) failure to package the DNA properly; and (3) failure to organize the nuclear material properly after sperm penetration. It is concluded that either altered stimulation protocols or altered in vitro maturation conditions are needed to increase the average number of normal embryos available for transfer.