Abstract: Apart from preformed antifungal agents, induced resistance to diseases can be obtained by stimulating of elicitors such as oxalic acid, microbial metabolites, heat or UV radiation. It will probably be a new way for storase of fruits if these agents are elucidated and used for biological control of postharvest diseases. Specific analytical methods are required to track them. The current method is that the tissue of fruit flesh is smashed and homogenized in a proper solvent, the active component is isolated and purified by chromatography and /or electrophoresis. The structure is elucidated by NMR, X_ray diffraction and spectrometric analysis. There are three ways to test the activity of the antifungal substances: thin_layer chromatography bioassay; spore/slide germination assay; and agar cup plate method. The compartmentation of the active compounds is followed by histological chemistry, which is benefited from immunofluorescence microscopy, immunogold labelling techniques and radio autographic analysis.