Pseudopregnancy, an induced physiological state in the rat which mimics the rodent's luteal phase, can be used to assess the impact of chemicals on the luteal phase of female animals. Female rats can be induced to be pseudopregnant by a variety of methods and assessment of the successful initiation and maintenance of pseudopregnancy is accomplished via vaginal cytology. The decidual cell response is a technique in which pseudopregnant rats undergo a surgical treatment of their uteri to induce uterine differentiation and proliferation. This results in massive tissue growth which mimics the response of the uterus during normal blastocyst implantation. Measurement of decidual growth during chemical treatment can be used to assess both hormonal status and uterine function. Uterine weight serves as a sensitive measure of the success of the decidual cell response.