Hunshandake Sandland is one of the biggest areas of semi-desert in China. It is also the primary source of sandstorms affecting Beijing and Tianjin. In recent years, scientists and the Chinese government have paid increased attention to the ecological restoration and reconstruction of the Hunshandake Sandland. To restore the vegetation of this region, the primary problem is how to control the populations of rodents.The striped hamster (Cricetulus barabensis) is a widely distributed species in the grasslands of Inner Mongolia. Striped hamsters like to eat plant seeds, which account for 70% of all their food. As a result, this animal has a negative impact on the restoration of vegetation on sandy land. It is necessary to find an effective way to control their population. Traditional chemical rat poisons can kill most individuals of a population in short time. However, thanks to their high reproductive ability, rodent populations are able to recover rapidly. Moreover, traditional chemical rat poisons pollute the environment and hurt nontarget animals at the same time.EP-1 is a new type of contraceptive compound, the main ingredients of which are levonorgestrel and quinestrol. EP-1 does not kill its target animals; instead, it affects the female reproductive system but the animals are able to recover from the damage. Laboratory experiments have shown that EP-1 has a remarkable impact on controlling the reproduction of rodents. Moreover, EP-1 has little effect on nontarget animals. Environmental pollution from EP-1 is also less than that from traditional chemical rat poisons.To test the effect of EP-1 on reproduction in the striped hamster, EP-1 baits were placed in the Hunshandake Sandland in April 2003. We chose four plots: two were baited and the others were control areas. Monthly trapping censuses were conducted to monitor the reproductive parameters of the rodent population during June to October. EP-1 did not influence the sex ratio of the striped hamster, and no significant differences were observed in the proportions of male hamsters between the baited and control areas (Student's t test, P < 0.05). EP-1 baiting obviously influenced the age structure of the striped hamster population, as the proportion of juvenile animals found in the baited area was only 40%-50% of that in the control area (Student's t test, P < 0.05). This impact lasted for more than 4 months. EP-1 baiting obviously influenced reproductive parameters. In the baited areas, EP-1 caused damage to the uteri of 70%-80% adult female hamsters, and in June 100% of the uteri were damaged. The organs turned black and uterine cysts were evident. This impact lasted for more than 5 months. Moreover, EP-1 baiting significantly reduced female fertility as no pregnant females were found in baited areas in June. The pregnancy rates in the baited areas were also very low in July and August: significantly different from the control area (Student's t test, P < 0.055). Litter sizes in the baited area were also influenced by EP-1 and were significantly lower than in the control area (pooled Student's t tests, P < 0.05). The impact of EP-1 on these rodents lasted for more than 4 months after a single baiting in spring, suggesting that it can influence the whole breeding season of this species. This fertility control effect might be related to the foraging behavior of striped hamsters. The impact of EP-1 baiting on the hamster populations declined with time, suggesting that female hamsters might be able to recover from the damage caused by EP-1. This recovery might also be explained by dispersal of the hamsters.