I studied infection, multiplication, and movement of eight plant viruses in both protoplasts and plant tissues with fluorescent antiserum, electric microscopy, bioassay, and rocket immunoelectrophoresis. New virus multiplication system in protoplasts was established and some differences of reaction between plant tissue and protoplast were discovered. For example, the dark-green area in Tobacco mosaic virus infected tobacco leaves shows resistance against re-inoculation, but the virus could multiply in protoplasts from the area. I studied on relation between chemical structural and its activity. Then a new compound, MON-24000 (thifluzamide) was found. This was a specific fungicide on Rhozoctonia solani. It is sold all over the world including Colombia (trade name: Pulsor). My themes are 1) to find antivirals from native plants extract or microorganisms and 2) isolation and identification of plant virus on lettuce, garlic, pea, uchuva, achila, and arracacha etc. Some virurs which were not reported in Colombia were found and started the research to control them.