Background: The use of Lewis inbred rats in embryonic tissue transplantation experiments can present a challenge because of the fertility problems associated with the strain that require large production colonies to harvest sufficient tissue for the experiments, but this practice goes against the principle of reduction. Purpose: order to maximize the fertilization of apt females an intrauterine artificial insemination technique (IUAI) was standardized in a Sprague Dawley outbred strain and later applied to the Lewis inbred colony. Methods: 41 Lewis rats to which estral stage determination was performed by impedance reading of the vaginal wall were inseminated. A midventral laparotomy was performed, the ovarian third of both uterine horns were located and gently elevated, and 350 µl of spermatozoid/0.9% saline solution were injected in each horn. Results: Even though the IUAI proved to be effective for use in outbred Sprague Dawley rats under these experimental conditions (average 5.08 embryos) at the time of sacrifice only 12 Lewis females (29.3%) were carrying embryos and the average embryos collected per female were 2.3. Conclusion: When the intrauterine artificial insemination technique was applied to the Lewis strain the number of pregnant females or the average embryo yield did not increase when compared to natural mating and therefore we do not recommend its use for this purpose.