The effects of MBC, applied as carbendazim (Bavistin) or thiophanate-methyl (Topsin-M), on several physiological processes in gherkin leaves were examined. In the experiments the following variables were introduced: a. the cultivars used were cv. 'Levo', which is susceptible to Sphaerotheca fuliginea, and cv. 'Milkus', which is resistant to this fungus, b. the plants were either left uninoculated or inoculated with Erysiphe cichoracearum or Sphaerotheca fuliginea, c. the fungicides were either applied as a soil drench or mixed through the soil, d. the time of treatment was either 15 or 36 days before inoculation. Using various combinations of these variables, the effects of MBC on chlorophyll content, oxygen evolution from isolated chloroplasts, monosaccharide (that means fructose, m-and ~-galactose and m-and B-glucose) content and fresh weight of leaves were estimated; in addition, in inoculated plants the disease was recorded. In the analyses, older and younger leaves were studied as two separate groups. On the basis of the results, the hypothesis is put forward that MBC might act as a plant growth regulator.