The usefulness of ion accumulation patterns, leaf chlorophyll content, and delayed fluorescence of plant leaves as indicators of toxicity due to chemical stress is illustrated in this paper. Using plants as bioassay tools, these parameters can often be used to detect plant stresses rapidly and in advance of visible symptoms (pre-symptom diagnosis). They can also be used to distinguish and define the type and nature of chemical toxins present in a given substrate. Central to the use of plants as bioassay tools for toxicity assessment is the selection of appropriate species. The data presented here for the ion accumulation patterns and the chlorophyll content illustrate the genotypic variation in soybean indicated by the tolerance of the variety Manchu and the sensitivity of the Williams variety to sodium chloride (NaCl) and potassium chloride (KCl) stresses. Electrical conductivity measurements of leaf extracts have shown highly significant differences between Manchu and Williams; conductivity of leaf extracts in Manchu was significantly lower than Williams within the range of 10 to 40 mM of NaCl. Varietal and salt concentration differences were also highly significant for the concentration of chloride in the leaves beginning with stress levels of 20 mM NaCl or KCl. In Williams, chlorophyll concentration in leaves of two-week old plants declined significantly with increase in NaCl or KCl stress, the decline being concentration dependent. Highly significant differences in leaf chlorophyll were noticed between Williams and Manchu at various salt concentrations. The data presented for the delayed fluorescence technique show distinct patterns of leaf images under different stresses. The differences between stressed and nonstressed plants was evident for all the four parameters (conductivity, chlorophyll, chloride, delayed fluorescence), at certain stress levels, at a time when visible symptoms of chloride or sodium toxicity were not apparent, indicating the potential for pre-symptom diagnosis of chemical stresses in plants using these measures.