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: In 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. Antecedentes: El uso de ratas endocriadas Lewis en experimentos de trasplantes puede representar un reto, por los problemas de fertilidad asociados con esta cepa, que implican mantener colonias de produccion grandes, a fin de poder recolectar suficiente tejido para usar en los experimentos; sin embargo, esta practica va contra el principio de reduccion. Proposito: Estandarizar el protocolo de inseminacion artificial intrauterina (IAIU) en una cepa exocriada Sprague Dawley y posteriormente aplicarla en la colonia de ratas Lewis, para maximizar el numero de hembras aptas fertilizadas. Metodos: Se inseminaron 41 ratas Lewis a las que se les habia determinado el estro por medio de impedancia vaginal. Se realizo una laparotomia medioventral para localizar y exponer el tercio ovarico de los cuernos uterinos, los cuales fueron cuidadosamente elevados y 350 μl de una solucion de espermatozoides/suero fisiologico al 0,9 % se inyecto en cada uno de los cuernos. Resultados: Bajo las condiciones experimentales presentes, la tecnica de IAIU resulto efectiva en la cepa exocriada (promedio de 5,08 embriones). Al momento del sacrificio solo 12 hembras Lewis (29,3 %) eran portadoras de embriones con un promedio de 2,3 embriones por hembra. Conclusion: Cuando se aplico la tecnica de inseminacion artificial intrauterina a la cepa de ratas Lewis, el numero de hembras prenadas o el promedio de embriones no aumento en comparacion con los resultados obtenidos por medio de cruces naturales. Por consiguiente, no recomendamos la aplicacion de esta tecnica para el proposito planteado.