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Commercial strains of Trichoderma show erratic results on soil diseases in northern Chile. Tolerance and antagonistic capacity were assessed in 10 isolates of native Trichoderma spp. and a commercial bioformulate of exogenous strains under saline-boric conditions. The following treatments were used in in vitro tolerance tests: APD amended with 8, 15 and 20g.l(-1) NaCl and the same three doses of NaCl + 15mg.l(-1) boron. Cation content of the three most tolerant isolates was measured. The antagonism and growth in vitro of Trichoderma vs F. oxysporum in APD with 8g.l(-1) NaCl were evaluated. In addition, a test in tomato plants inoculated with F. oxysporum and Trichoderma, and irrigated with 8g.l(-1) NaCl and 15ppm boron was made. In vitro ANOVA, Tukey test and t (student) test were used on the growth of F. oxysporum. Kruskall-Wallis and Mann-Witney U tests were used in the case of plants; all with 95% confidence. Native strains were the most tolerant (p <= 0.05); higher levels of Na+ in the mycelium were associated with salinity tolerance. Saline solutions and boron further reduced growth and sporulation. F. oxysporum showed higher growth in a saline medium (p <= 0.05). Native Trichoderma can protect plants from Fusarium infection in saline-boric environment and an antagonistic inter isolated activity may exist. In the north of Chile strains that are highly tolerant to saline-boric conditions exist. The native strains are the best alternative for the control of Fusarium in saline and arid zones.