The evaluation of the tomato genotypes response to heat or/and drought stress in order to assess their adaptation potential to the environment and depending on the some genotypic, physiologic, biochemical parameters. Tomato germinated seeds were exposed to heat or/and drought stresses. The histochemical presence of Reactive Oxygen Species (ROS) in radicle was evaluated by microscopic analyzes. Depending on the particularities of the genotypes, different reactions to the heat and drought stress action were established, expressing high, medium or low resistance. It was found that drought stress has a stronger inhibitory impact on radicle growth, compared to heat stress, being ahead of their action in the complex. The analysis after 10 days of postthermal action established that in plants exposed to stress, the root length remains significantly shorter than the control variants by about 30-70% and the lateral roots often exceeded the length of the main root. Microscopic analyzes of the radicles established a slightly different distribution of ROS in the meristem, elongation and maturation zone, as well as in the collet (RootHypocotyl junction), depending on the genotype and/or the stress factor. Thus, from 6 analyzed genotypes, in 3 the length of the segment with ROS accumulations in the meristem zone was between 63.7-78.0 μm, and in the rest 10.9-14.3 μm. In the variants exposed to heat, drought or mixed stress, 24 hours after stress action the lack of ROS accumulations in the meristem area was established; only in solitary cases accumulations represented 0.5-2 μm. In the variants exposed to drought stress, ROS accumulations were mainly on the radicle surface (epidermis), more consistent accumulations were in the collet and very small quantities inside the root (cortex, stele). In the case of heat stress, there were accumulations of varying intensity (depending on genotype) in the elongation and maturation zones, the collet, along the vascular bundles and/or in the space of the cortex and stele, and absent in the epidermis. The mixed stress determined the total lack of ROS in the meristem zone, minor accumulations along the radicle, the maximum amount being attested in the second half of the collet. There was a differentiated reaction of genotypes to the action of heat or/and drought stress by the intensity of root growth. The manifestation of ROS in the radicles was a specific response depending more by the stress factor and less by the genotype.