To investigate the association of human chorionic gonadotropin (HCG) level on day 3 of embryo culture with embryo development. Wang, Haiying Zhang, Renli Han, Dong Liu, Caixia Cai, Jiajie Bi, Yanling Wen, Anmin Quan, Song Our results suggest that TSA-treatment does not improve blastocyst development of rabbit- human iSCNT embryos and that abnormal histone deacetylation-reacetylation changes in iSCNT embryos may account for their poor blastocyst development. We also found evident time-dependent histone deacetylation-reacetylation changes in rabbit-rabbit cloned embryos, but not in rabbit- human cloned embryos from fusion to 6 hr after activation. After treatment with TSA for 6 hr during activation, we found that the blastocyst rate of rabbit-rabbit cloned embryos was more than two times higher than that of untreated embryos however, the blastocyst rate of TSA-treated rabbit- human interspecies cloned embryos decreased. Herein, we observed the effect of TSA on the development of rabbit-rabbit intraspecies and rabbit- human interspecies cloned embryos. However, the incomplete nuclear reprogramming and the low blastocyst rate of iSCNT are still big problems. The interspecies somatic cell nuclear transfer (iSCNT) technique for therapeutic cloning gives great promise for treatment of many human diseases. Shi, Li-Hong Miao, Yi-Liang Ouyang, Ying-Chun Huang, Jun-Cheng Lei, Zi-Li Yang, Ji-Wen Han, Zhi-Ming Song, Xiang-Fen Sun, Qing-Yuan Chen, Da-Yuan Trichostatin A (TSA) improves the development of rabbit-rabbit intraspecies cloned embryos, but not rabbit- human interspecies cloned embryos.