Vibration measurements were made of the basilar membrane (BM), limbi and columella footplate (CFP) of pigeon using the Mössbauer technique. Recordings were located at 0.23-1.33 mm from the basal end of the BM. The existence of a travelling wave mode, propagating from base to apex, was established for papillae in apparently good physiological condition. For these papillae the characteristic frequency (CF) of the BM isovelocity (0.08 mm X s-1) response was an exponential function of distance with a frequency mapping constant of 0.91 +/- 0.10 mm (equivalent to 0.63 +/- 0.07 mm X oct-1); BM CF at the base was 5.95 +/- 0.65 kHz. Travelling wave motion was not demonstrated for papillae in poor physiological condition; tonotopy of BM CF was still evident, although the correlation with distance was less (1.08 +/- 0.30 mm X oct-1; 4.35 +/- 0.73 kHz at the base). BM motion was linear and the isovelocity responses were less sensitive and less sharp than single unit threshold tuning curves: for papillae in good physiological condition the SPL at BM CF at 0.08 mm X s-1 was 51 +/- 6 dB SPL; Q10 dB was 1.24 +/- 0.38; high- and low-frequency slopes were 20 +/- 6 dB X oct-1 and -14 +/- 4 dB X oct-1, respectively. The response of the BM relative to the CFP for papillae in good physiological condition was reminiscent of a second order resonant system with damping constant of 0.33 +/- 0.06 and group delay at BM CF of 0.89 +/- 0.36 periods.