The ir absorption of gaseous 15NH 3 between 510 and 3040 cm -1 was recorded with a resolution of 0.06 cm -1. The ν2, 2 ν2, 3 ν2, ν4, and ν2 + ν4 bands were measured and analyzed on the basis of the vibration-rotation Hamiltonian developed by V. Špirko, J. M. R. Stone, and D. Papoušek ( J. Mol. Spectrosc.60, 159-178 (1976)). A set of effective molecular parameters for the ν2 = 1, 2, 3 states was derived, which reproduced the transition frequencies within the accuracy of the experimental measurements. For ν4 and ν2 + ν4 bands the standard deviation of the calculated spectrum is about four times larger than the measurements accuracy: a similar result was found for ν4 in 14NH 3 by Š. Urban et al. ( J. Mol. Spectrosc.79, 455-495 (1980)). This result suggests that the present treatment takes into account only the most significant part of the rovibration interaction in the doubly degenerate vibrational states of ammonia.