We have measured the far infrared optical constants of MDA-00-3461 at 25 degrees C by using terahertz time-domain spectroscopy. The extraordinary and ordinary refractive indices of MDA-00-3461 are n(e) approximate to 1.74 and n(o) approximate to 1.54, or a birefringence of 0.20 from 0.3 to 1.4 THz. The extinction coefficient of MDA-00-3461 is relatively small. There are no absorption peaks in the frequency range investigated.