The roe deer blastocyst is in diapause between August and December, after which time it expands and elongates rapidly before implantation. Blood samples were taken from 30 animals to define temporal changes in reproductively important hormones to investigate the physiological cues present at embryo reactivation. In 15 of these animals, changes in uterine and conceptus protein synthesis and secretion, and luteal progesterone release during diapause and reactivation, were assessed after culture of these tissues in vitro. Oestradiol concentrations remained low during diapause (1.07 ± 0.4 pg ml-1) and expansion (1.2 ± 0.4 pg ml-1) but increased by 30 times at trophoblast elongation (49.17 ± 0.37 pg ml-1). Prolactin remained at basal concentrations (4.69 ± 0.86 ng ml-1) and increased after implantation (12.34 ± 2.71 ng ml-1). Peripheral progesterone concentrations and luteal progesterone release remained constant throughout diapause, reactivation and implantation (peripheral progesterone: 3.82 ± 1.97 ng ml-1; luteal progesterone: 6.72 ± 0.81 ng mg-1 protein). Incorporation of a radiolabel into conceptus secretory proteins increased by four times at expansion compared with diapause, whereas incorporation into endometrial secretions remained constant. At elongation, incorporation into endometrial secretions increased two times and conceptus secretions increased 32 times. Two-dimensional electrophoresis and fluorography showed that the profile of endometrial secretory proteins was constant until implantation when qualitative changes were evident. Although a role for an endocrine maternal trigger of reactivation from diapause cannot be dismissed, these data provide no supporting evidence and indicate that the conceptus itself may drive reactivation.