Optimal conditions of the greenhouse, with soilless culture in which the plants are optimally supplied with water and nutrients, stimulate their growth and development, and achieve high yields and quality. Nevertheless, plants go through stressful periods during their life cycle, which is why biostimulants are increasingly used to support plant growth and development, increase their resistance to diseases, pests and environmental stressors, and improve nutrient absorption. Therefore, a study was conducted to determine the effect of biostimulants on the yield components of hydroponically grown tomatoes. The experiment was conducted at the experimental field of the Department of Vegetable Crops at the Faculty of Agriculture in Zagreb during the period from March 1, to August 28, 2019. Two tomato cultivars 'Vasanta' and 'Alamina', treated with biostimulants, Actiwave, Humistar, Phylgreen were tested and compared to the untreated control. The yield components were certainly affected by the greenhouse microclimatic conditions, which varied considerably during the vegetation and were often outside the optimal values. The tested cultivars differed significantly in the number of marketable fruits per plant and the share of non-marketable fruits, while in the marketable yield no significant differences were found due to different fruit sizes. The applied bistimulants affected the number of marketable fruits per plant, with significant differences found only between the two applied biostimulators, while at the same time, no significant differences were found in the marketable yield and the share of non-marketable fruits. The highest marketable yield was achieved by cultivar 'Alamina' with the use of biostimulants Phylgreen (13.84 kg/plant) and Humistar (13.34 kg/plant), while on control plants of the same cultivar, ie on plants treated with Actiwave, a significantly lower yield was recorded (10.76 and 10.62 kg/plant). In all tested interactions, the share of non-marketable fruits was higher than 25% (from 26.26 to 43.16%) with established highly significant differences.