The aim was to examine vegetative and generative parameters of 15 peach and nectarine cultivars planted 2003 on the rootstock Cadaman organically cultivated in the experimental orchard of the institute in Vienna. The susceptibility to diseases, especially Taphrina deformans and Monilinia ssp., as well as to frost damage was analysed. Furthermore, characteristics of blossom, growth (circumference of the stem, type and length of shoots and colour of leaves) and yield (amount, quality and time of ripening) were examined. In 2007, 30 fruits per cultivar were tested for weight, shape and colour of the fruit, firmness of the flesh and characteristics of the stone, content of vitamin c, soluble dry matter, titratable acidity and the holistic quality parameter p-value. A small sample of fruits was tasted and the biophoton radiation analysed. Some of the cultivars showed significant differences in parameters of bloom and growth. There was no relation between the beginning of bloom and the extent of damage of frost. There were also differences concerning ripening time and yield parameters. Diamond Princess was infected heavily by Taphrina deformans, in opposite Amsden and Weingartenpfirsich Eibesthal. The fruit quality parameters were influenced by the culivar. The fruits which were chosen for the biophoton measurement were different their stage of maturity, state of health and position on the tree. As a consequence the results must be regarded with care. Redhaven, Sweethaven, Mireille and Redcal can be recommended for organic production and Benedikte, Nectared 6, Red Robin and Royal Glory partly recommended. Royal Gem, Diamond Princess, Early Devil and Weingartenpfirsich Eibesthal are not suitable.