Damage to fruit of eight accessions and cultivated varieties of tomato by natural infestations of beet armyworm,Spodoptera exigua(Hübner), in Southern California ranged from 0.1 to 10%. This field damage was significantly correlated with 9-d weight and survival ofS. exigualarvae reared to pupation from third instar in the laboratory on fruit of these tomato test entries. Two accessions ofLycopersicon esculentumvarietycerasiformeand one small-fruited cultivated variety ofL. esculentumsustained lowest damage in the field (1–50% of susceptible controls).S. exigualarvae had reduced survival and reduced 9-d weight (≈20% of susceptible controls). Time to pupation was also increased on these three lines (30% greater than controls). The resistant fruits had high concentrations of total glycoalkaloids in the fruit tissue (5.4 to 25.4 mg/g dry weight versus 1.8 mg/g in a susceptible fruit) and this may have been the basis of the antibiosis. Phytosterol concentrations in the fruits were not sufficiently high to potentially alleviate glycoalkaloid toxicity. In binary choice tests between fruit and foliage of the most resistant line,L. esculentumvarietycerasiformeLA 1320, larvae ofS. exiguafed on fruit 70% less than larvae in choice tests between the fruit and foliage of susceptible ‘VFN 7718’. Larval nonpreference for fruit apparently contributes to resistance in LA 1320. The resistance toS. exigua, of LA 1320 predicted by this mechanism, is close to observed levels of resistance in the field.