The electron transfer processes occuring in SDS chlorophyll--protein complexes of photosystem I were studied by flash photolysis. Transient species with lifetime about 5.10(-5) sec were found to be produced on flash excitation of complex buffer solutions. The transient absorption spectrum of the short-lived species measured in the absence of SDS resembles that of P+700. This spectrum was similar with that of chlorophyll anion radical (chl-) when SDS was added to the solution. It is assumed that the charge separation in chlorophyll--protein complexes leads to formation of the primary reduced acceptor X-. The chl-species arised as a result of electron transfer from X- to monomeric form of chl a.