This review article summarizes all the recent informations concerning the mutagenic effects of psoralen monoadducts and crosslinks in bacteria. Like other DNA damaging agents, psoralens are mutagenic, recombinogenic and carcinogenic. Among these genotoxic effects, the mutagenic action is probably the most-well described. After a short survey of the repair of monoadducts and crosslinks in bacteria, this article will review some results concerning (i) the evaluation of the relative mutagenicity of monoadducts and crosslinks and (ii) the nature of the mutations induced by both random and site specific modification of plasmid or phage DNA.