Survival following cryopreservation of fresh and aged human oocytes by the propanediol (PROH) procedure was observed in 51 and 73% of oocytes respectively, immediately after thawing. This survival was reduced in both types of oocytes at the time of insemination (3-4 h) to 41% in fresh and 61% in aged oocytes. Insemination of the cryopreserved and control oocytes with spermatozoa from one donor resulted in total fertilization rates similar to our in-vitro fertilization (IVF) rate for non-male factor patients. The normal fertilization rate for fresh cryopreserved oocytes was slightly lower (46%) than the rate for IVF oocytes (59%) (P < 0.05), while the abnormal fertilization rates were not significantly different (16 and 15% respectively). In contrast, a reduction in the normal fertilization rate was observed for the aged cryopreserved oocytes (13%) compared to the IVF rate (P < 0.001). Associated with this was an increase in the abnormal fertilization rate for the aged cryopreserved oocytes, which was significantly higher (47%) than the IVF rate (15%) (P < 0.001). Significant differences in the total and normal fertilization rates were observed between cryopreserved oocytes obtained from cohorts with < or = 27 (total: 84%, normal: 68%) and > 27 oocytes (total: 55%, normal: 33%) (P < 0.05). Fertilized oocytes and oocytes with abnormal or absent spindles were examined for chromosomal loss and no stray chromosomes were observed in any of these cryopreserved oocytes (n = 137). In the cryopreserved oocytes which had undergone normal fertilization, four scorable karyotypes were achieved and in all of these two sets of 23 chromosomes were observed.