The consequences of the elevated CO2 and the elevated CO2 with an increased temperature on rhizosphere of perennial ryegrass were investigated. Ryegrass grown in the loamy soil treated with two different doses of mineral N (160 and 530 kg N.ha(-1).year(-1)) was continually kept in experimental climate conditions for approximately two and half years. The amount of C and N compounds (total extractable C, carbohydrate, reducing sugars, ninhydrin reactive N and ammonium N), fluorescein diacetate (FDA) hydrolytic activity, proteolytic activity of extracellular enzymes and the composition of microbial communities (CFU on elective media) were measured 15, 20 and 27 months of plant growth in the experimental conditions. The contents of extractable C and carbohydrates increased with plant age in all climate conditions, while the contents of reducing sugars, ninhydrin-reactive N and ammonium N did not. We found significant positive effect of the experimental climate conditions on the contents of C and N compounds and on FDA activity after 15 months of ryegrass growth. At the end of the experiment, after 27 months of plant growth in the experimental conditions, all these parameters were affected negatively. The decrease of the values was slowed by N fertilisation but not eliminated. Proteolytic activity was significantly higher in the experimental climate conditions in most sampling. The numbers of CFU on various media were decreased in the elevated CO2 conditions in June 1994 and 1995, and in the elevated CO2 with increased temperature conditions in June 1995. Again, N fertilisation did not entirely eliminate the negative effect of the experimental climate conditions. Our results demonstrate that the positive effect of changing climate on the content of organic compounds in rhizosphere and on activity of rhizosphere microflora of ryegrass was only a short-term one.