We noted varying success rates with IVF on a month-by-month basis from 1998 through 1999. During that interval, we had no control over the room temperature and results appeared to be affected by seasonal temperature fluctuations. Since 2000, we have maintained a constant temperature of 25°C in our operating and culture rooms throughout the year. During that time, our pregnancy rate has been significantly higher than in previous years. Specifically, we noted an improved pregnancy rate during the summer season (June and July). A constant room temperature of 25°C significantly enhances the efficacy of in-vitro fertilization.