Many researchers are reluctant to administer analgesia after rodent embryo transfer, primarily out of concern that analgesia will affect embryo implantation. According to the Animal Welfare Act and the Guide, however, embryo transfer constitutes major survival surgery and is likely to cause pain and distress despite its minimally invasive nature. The authors examined the effects of a single dose of the analgesic buprenorphine on mice that underwent embryo transfer. In mice treated with buprenorphine, the number of viable implanted embryos was typically equal to or greater than that in untreated mice. All mice seemed quiet, alert and active after surgery.