Free-field detection by normal and monaural ferrets of a 500-Hz tone presented over 1 laterally placed loudspeaker and partially masked by narrow-band noise from 2 sources was studied at 2 angular separations of the noise sources (0 degree and 180 degrees). Monaural listening was achieved either by plugging 1 ear canal or removing 1 cochlea. Normal ferrets showed an improvement in detectability of the tone when there was a 180 degrees separation between the noise sources. This unmasking of the tone was abolished in both groups of monaural ferrets, suggesting that the unmasking was due to binaural processing. The development of an animal model demonstrating free-field binaural unmasking, in a species other than humans, will allow investigation into the functional consequences of experimental hearing loss.