The picosecond and nanosecond resonance Raman spectra of bacteriohodopsin (bR) have been determined by microbeam and flow techniques. The 40-ps pulses were generated by a synchronously pumped mode-locked, cavity-dumped dye laser. The pulse width is extended to 15 ns by CW pumping the cavity-dumped dye laser. The spectrum of the picosecond transient in the fingerprint region resembles the bR/sub 550//sup DA/ spectrum. The retinal in the latter species is believed to be in the 13-cis configuration. These results suggest that the retinal changes from an all-trans- to a 13-cis-type of configuration in less than 40 ps (the pulse width of the photolyzing laser). Slight differences are observed between the picosecond and nanosecond retinal spectra. These observations suggest that more than one species exist in the 40-ps to 100-ns time scale.