We have measured and analyzed rotational transitions of N2O in the following vibrational states, 01(1e,f)0, 02(0,2e,f)0, 03(1,3e,f)0, 00(0)1, 01(1e,f)1, and 10(0)0. The NAIR terahertz spectrometer was used to measure the frequencies of transitions in the range J = 25 <-- 24 to J = 31 <-- 30 with accuracies of +/-0.020 MHz in most cases. These measurements were fit, along with other microwave and infrared measurements involving the same states, to obtain improved rovibrational term values for those vibrational states. It is shown that the measurements can be fit with fewer constants if both l-type resonance and the Fermi resonance among the levels 00(0)1 and 02(0,2)0 or 01(1)1 and 03(1,3)0 are included in the least-squares fit. These measurements also contribute to improving the N2O wavenumber calibration standards for the infrared region. Copyright 1999 Academic Press.