A new image instrumentation system for quantitative analysis of the rapid change in intensity of chlorophyll fluorescence during dark-light transition (CFI, chlorophyll fluorescence induction), which is a sensitive indicator of the various reactions of photosynthesis, was developed and its performance was evaluated. This system made it possible to resolve CFI at any small leaf area (about 1 square millimeter) of a whole leaf when the plant was illuminated by blue-green light at more than 50 micromoles photons per square meter per second. In order to test the usefulness of this system, we applied it to analyze the effect of SO(2) on photosynthetic apparatus in attached sunflower leaves. Dynamic CFI imaging over the whole single leaf, where there was no visible injury, indicated not only the local changes in photosynthetic activity but also the site of inhibition in photosynthetic electron transport system in chloroplasts. The new instrumentation system will be useful for the analytical diagnosis of various stress-actions on plants in situ.