The formation of bathorhodopsin (formerly prelumirhodopsin) was first observed by Yoshizawa and Kiti, [ 11 who irradiated cattle rhodopsin at liquid nitrogen temperature (77 K). Afterwards, the spectra of batho-intermediates in various animals were measured by low temperature spectrophotometry [2]. Therefore it is generally believed that bathorhodopsin is the earliest photoproduct in the photobleaching process of rhodopsin. Recently it was found that irradiation of cattle [2] or squid rhodopsin [3] at liquid helium temperature yielded two thermolabile photoproducts hypsorhodopsin @,a,: cattle 430 nm, squid 446 nm) and bathorhodopsin (A,,,: cattle 543 nm, squid 534 nm). Now the question arises: which is an earlier photoproduct of rhodopsin, hypsorhodopsin or bathorhodopsin? In order to elucidate this problem, we tried a picosecond laser flash photolysis of squid rhodopsin using a 347 nm light pulse from a mode locked ruby laser.