In order to provide a better understanding of the response to salt and water stress in tomato seeds and plants of the species Solanum chilense, S. peruvianum, S. lycopersicoides and S. lycopersicum cv. Poncho Negro, the effects of NaCl and polyethylene glycol (PEG) on germination and plant biomass were analyzed at similar iso-osmotic conditions. The seeds were placed to germinate in a growth chamber at alternating temperatures of 20/25 degrees C applied for 8 /16h. Plants were grown in pots. The biomass of all populations of tomato decreased with 100mM NaCl and equivalent iso-osmotic PEG (-0.38MPa). At levels of 150mM NaCl and equivalent iso-osmotic PEG (-0.571MPa) biomass effects are more detrimental with PEG (-0.57MPa). Higher biomass recorded in plants treated with NaCl compared to treatment with PEG, so that there is an effect of ionic salt stress. The stress of 100mM NaCl and equivalent iso-osmotic PEG is more severe in seed than in plants. But with levels of 150mM NaCl and the equivalent iso-osmotic PEG the most damaging effects are observed in the seeds. The wild species S. peruvianum, found growing in the valley of Lluta, Chile, along with the cultivated species S. lycopersicum cv. Poncho Negro, were shown to have greater tolerance to 100mM NaCl and the iso-osmotic equivalent of PEG.