A set of introgression lines from S. peruvianum PI 126944 into the genetic background of cultivated tomato (S. lycopersicum) is being developed. Several generations were derived from three interspecific hybrids previously obtained. A lot of crosses and embryo rescue were required to obtain until the third backcross, due to the high incompatibility existing between tomato and PI 126944. Crosses between F1 plants allowed the obtaining of a pseudo-F2 generation. The same procedure was followed until pseudo-F6 generation. Additional crosses between plants of different generations were made in order to increase progeny. Among a total number of 263 molecular markers tested, 105 resulted polymorphic between tomato and PI 126944. This set of polymorphic markers consisted in 90 Simple Sequence Repeats and 15 Cleaved Amplified Polymorphic Sequences. Generations available were genotyped with these markers, observing a progressive reduction in the S. peruvianum genome in the most advanced. A reduction of incompatibility was achieved as a consequence of the S. peruvianum genome reduction. In addition, S. peruvianum genome was almost completely represented considering the different plants of the most advanced generations, so the set of ILs will be basically developed from them. Tomato yellow leaf curl virus (TYLCV) and Tomato spotted wilt virus (TSWV) resistance was evaluated in some generations, having been successfully introgressed and expressed into tomato background.