The infrared vibration-rotation bands of SeH have been measured in the X(2)Pi ground state using a Fourier transform spectrometer. The bands were observed in a microwave discharge of a mixture of H(2) and Se in the presence of He. The rotational structure of the 1-0, 2-1, 3-2 bands of the X(2)Pi(3/2) spin component and the 1-0 band of X(2)Pi(1/2) spin component has been observed in the 1800-2600 cm(-1) region. The principal ground state molecular constants obtained are omega(e) = 2421.7153(234) cm(-1), omega(e)x(e) = 44.6012(110) cm(-1), omega(e)y(e) = 0.20697(236) cm(-1), B(e) = 7.899187(696) cm(-1), alpha(e) = 0.220749(399) cm(-1), and r(e) = 1.464319(64) Å. This work is the first determination of the equilibrium molecular constants of the X(2)Pi state of SeH. Copyright 2000 Academic Press.