Three populations of Belonolaimus longicaudatus from Gainesville, Fuller's Crossing, and Sanford, all in Florida, were tested for parasitism on Citrus jambhiri (rough lemon), Arachis hypogaea ('Early Runner' peanut), Fragaria sp. ('Florida 90' hybrid strawberry), and Lycopersicon esculentum ('Rutgers' tomato). The three populations were found to be three different physiological races because: (i) the Fuller's Crossing population reproduced well on and caused injury to rough lemon and tomato but not strawberry; (ii) the Gainesville population reproduced well on and caused injury to peanut, strawberry and tomato but not on rough lemon; (iii) the Sanford population reproduced well on and caused injury to peanut, reproduced well on tomato, but neither reproduced upon nor caused injury to strawberry or rough lemon. Morphologically, females of the Sanford population have a lower "c" value and a greater number of tail annules than those of the Gainesville and Fuller's Crossing populations. Females and males of the Fuller's Crossing population had higher "a" values than those of the other two populations.