We obtained the absorption spectrum of the N intermediate that plays an important role in the proton uptake during the photocycle of bacteriorhodopsin. The reported spectra of N that: were reconstituted from the transient difference absorption spectrum depended on the assumed kinetic models such as sequential M --> N --> O reaction and M reversible arrow N reversible arrow O quasi-equilibrium In this work we measured the excitation spectrum of N by monitoring the characteristic absorption of Q (a photoproduct of N) at 664 nm. The lambda(max) and epsilon(max) of N were 559 +/- 3 nm and (4.30 +/- 0.75) x 10(4) M-1 cm(-1) respectively. The present spectrum is consistent with the results of the recent SVD analysis. This work provides independent evidence that Q is photochemically formed from N.