We examined mosquitofish. (Gambusia holbrooki) caught between January 1990 and December 1991 from 24 sites in northern Florida (USA), and preserved specimens collected from 32 sites throughout Florida between 1930 and 1978, for presence of the larval nematode Eustrongylides ignotus. We found 10 (42%) of the 24 recently-sampled sites in northern and central Florida had at least one larval nematode present in the fish; combining these data with results of previous work, 11 (15%) of 75 recently sampled sites throughout Florida had at least one nematode. By comparison, in the museum collections fish from only one (3%) of the 32 sites had the nematode, and none in northern Florida.