The reproductive physiology of female Djungarian hamsters (Phodopus campbelli) varies in several ways from that of more conventional laboratory models. In this study we investigated serum and pituitary levels of prolactin (PRL), LH, and FSH during preimplantation pregnancy. Data were collected from independent females every 2 h from 2200 h on proestrus through 0600 h on Day 5. PRL levels in serum showed a distinct, biphasic, nocturnal surge pattern. Levels during the light phase were low, with variable PRL during Day 2, when both estrogen and progesterone are at low levels in serum. FSH and LH levels in serum were determined twice daily. Elevated FSH and LH levels were found on Day 0 (proestrus). FSH then remained at a basal level while LH began to increase, with evidence for a daily rhythm in serum LH levels. Both FSH and LH accumulated in the pituitary over the first 4 days of pregnancy, although patterns were difficult to interpret. Data were consistent with a hypothesis that ovarian follicular development and preparation for a possible ovulation occur during preimplantation.