The absorption spectrum of NO in rare gas matrixes was restudied. The valence B2P(v',0) bands which, in the gas phase, show perturbations for v'>=7 due to homogeneous configuration mixing with the Rydberg C2P state, appear unperturbed up to v' = 10 in Xe, 12 in Kr, 14 in Ar, and 19 in Ne matrixes. The perturbations are shifted to higher energies due to the large blue matrix shifts experienced by the Rydberg states. They appear as irregular vibrational spacings, anomalous intensities, and modifications of the B2P(v',0) band profiles. The intensity patterns are qual. explained in terms of quantum-mech. interference effects. When resonant with a multiphoton Rydberg band, Fano line shapes appear in place of the sharp B(v',0) valence lines. The line shapes were simulated by the Fano theory assuming that only part of the Rydberg multiphonon quasicontinuum interferes with the sharp valence band. Good agreement is obtained with the exptl. spectrum and the fitted Fano indexes lie close to the calcd. ones. [on SciFinder (R)]