Objectives: Cellular fragmentation in human embryos is a poorly understood phenomenon. It has recently been hypothesized that fragmentation in these embryos is a consequence of programmed cell death (PCD) or apoptosis and that highly fragmented embryos have a poor prognosis for survival. The main objective of this work is to identify genes whose activation or suppression predict human embryo survival. In this study we examined the transcription of the apoptotic genes bax and bcl-2.Design: Using single-oocyte and single-embryo RT-PCR we characterized the mRNA expression of bax, a regulatory gene that promotes cell death and bcl-2, a regulatory gene which functions to enhance cell survival in various cell types.Materials and Methods: RNA was isolated from spare human oocytes (N= 10) and embryos (N=50) at various stages of development. The RNA was converted to single-stranded cDNA in the presence of random primers with reverse transcriptase. Nested primer PCR was performed with bax, bcl-2, and GAPDH primers.Results: The results show that bax mRNA is expressed at all stages of preimplantation human embryonic development implying that the transcripts are both maternal and embryonic. There are varying levels of bax mRNA expressed in different stages of oocyte maturation (GV, MI, and MII). The bax transcript was also present in 2-cell, 8-cell, 16-cell, compacted morula, and blastocyst stages.The bax mRNA was present in 1921 embryos. The abundance of the mRNA varied among day 4 embryos. Similarly, bcl-2 transcript was also expressed in 2-cell, 8-cell, 16-cell, and compacted morula stages but with much greater variability in message abundance. The bcl-2 mRNA was present in 1320 embryos, but only abundant in 420. As a result, we began to look at the bax/bcl-2 ratios to predict embryo survival. In 9 embryos from day 4 of development we found the following qualitative mRNA levels: 69 embryos had bax > bcl-2, 29 embryos had bax = bcl-2 and 19 had bax < bcl-2. The highly fragmented embryos had bax mRNA > bcl-2 while the normal embryos had bcl-2 mRNA either equal to or greater than bax mRNA.Conclusions: Since bcl-2 promotes cell survival its over-expression may be important for human embryo survival during culture in vitro. Our results show that 419 spare human embryos had abundant expression of bcl-2, and that these embryos were less than 15% fragmented. We also found that the ratio of bax/bcl-2 may be correlated to the degree of fragmentation in the human embryo. Moreover, the bax/bcl-2 mRNA ratio may be useful to predict human embryo survival. More experiments are in progress to determine if this result is sustained and whether the ratio can be applied as a diagnostic tool.