The different types of damage (synaptic anomalies, chromosome reorganizations and nucleolar fragmentation) observed in oocytes from female rat fetuses irradiated at 14, 16 and 18 days of gestation (d.g.), respectively, indicates the existence of a special sensitivity at the different stages of prophase to X-rays. At the highest dose (5 Gy), we observed a decrease in some of the synaptonemal complex indicators of chromosomal damage, probably reflecting a selection against cells with the highest degree of chromosome anomalies.