Nineteen interspecific hybrid breeding lines were tested for resistance to a TSWV isolate using enzyme-linked immunosorbent assay (ELISA) to check for presence of the virus after inoculation. These lines were all BC1F6 lines derived from L. esculentum crosses with seven L. chilense accessions. All of these lines had been selected for high tolerance/resistance to tomato mottle virus (ToMoV), a geminivirus [Scott et al., Bemisia 1995: Taxonomy, Biology, Damage Control and Management 30: 357–367 (1996)]. The initial TSWV screening indicated that eight of the 19 original lines had “possible” TSWV resistance. Seed from these selected eight lines were then planted and inoculated with TSWV ≈3 weeks after emergence. Three weeks later, ELISA results indicated that all plants from all lines were infected with TSWV. However, none of the plants from Y118 (derived from the LA 1938 cross) showed visual TSWV symptoms. The Y118-derived plants were allowed to grow for several months, and at no time developed significant visual symptoms of the virus. The consistent lack of TSWV symptoms prompted a second ELISA test on the Y118 plants, and the results indicated the plants were completely free of TSWV. Further tests were then initiated with F2 (L. esculentum × Y118) seed, and results indicate a single dominant gene is responsible for TSWV resistance. Data from this segregating population, including a molecular marker study which screened 800 randomly amplified polymorphic DNA (RAPD) primers, will be presented. Approximately two to five RAPD primers are possibly linked to TSWV resistance.