A population of the fernOsmunda regalisgrowing in a polluted river was investigated genetically. Previous studies documented a high frequency of postzygotically induced genetic and chromosome damage. This paper describes two categories of gametophytic mutants which occurred in the progeny of this population. A gametophyte phenotype which exhibited a maternal effect on the sporophyte generation when it was the female parent occurred in 7.8% of the spore sample. A gametophyte phenotype which could best be characterized as a neuter calluslike mass occurred in 6.6% of the spore sample. Studies of nearbyO. regalispopulations in non-polluted sites failed to document the presence of such phenotypes in the spore samples.