There is an increasing interest in the technique of using indicator plants as tobacco to detect and to monitor the ambient levels of photochemical oxidants. The bio-indicator plant "tobacco BEL W3" shows characteristic responses (visual foliair injuries) that are specific of ozone. The development of leaf necrosis is used to calculate the "Leaf Injury Index". This index does not give the absolute concentration of ozone in the atmosphere, but it provides estimates of relative levels of this pollutant. From the information given by the different bio-stations with tobacco (position, leaf injury index), it is easy to map the spatial and temporal distribution of ozone at ground level. The operation of plant bio-stations with tobacco is fairly fast, simple and economical since it does not require use of complex technological equipment. In conclusion, campaigns of environmental monitoring using tobacco could be organized on a wider geographical scale, and could also be used for educational and didactical purposes.