ABSTRACT. Oliveira J.P., Jacob J.C.F., Jesus V.L.T. & Silva P.C.A. [Influence of temperature and humidity in a equine embryo transfer program, in the Baixada Fluminense, Rio de Janeiro.] Influência da temperatura e umidade ambiente em um programa de transferência de embriões equinos, na Baixada Fluminense, Rio de Janeiro. Revista Brasileira de Medicina Veterinária, 37(2):158- 162, 2015. Departamento de Reprodução e Avaliação Animal, Universidade Federal Rural do Rio de Janeiro, BR 465, Km 7, Seropédica, RJ 23890-970, Brasil. E-mail: email@example.com This study aimed to evaluate the relationship between high environment temperature and humidity and reproductive rates in a equine embryo transfer program in Baixada Fluminense RJ. We evaluated the reproductive history of 60 donor mares and 111 recipient mares during summer of breeding seasons of 2008/2009, 2009/2010 and 2010/2011. Daily climatics data of environmental temperature (°C) and relative humidity (%) for the each breeding seasons were obtained from the web site of the National Institute of Meteorology (INMET), based on these data we calculated the temperature x humidity index (TUI) wich measures the thermal comfort zone. The reproductive parameters assessed were embryo recovery rate (RR) and pregnancy rate (PR). After the computation of reproductive and climatic data, these were compared to establish relationships between high temperatures and humidity on reproductive rates. There was a negative relationship between RR and high environmental temperatures, especially in the summer time, greater RR at 26°C (71%) and lower RR at 27°C (51.4%) (p <0.05). To PR there was a negative relationship to high environmental temperatures, the higher PR was obtained at 24°C (81.5%) and lowest PG (35%) at 27°C (p <0.05). We conclude that there are relationships between environmental variables and ET success.