This thesis describes an analysis of the possibilities and limitations of asymmetric somatic hybridization between tomato and potato. For this, nitrate reductase-deficient tomato mutants were isolated and characterized. It was shown that two of these mutations could be used as selectable markers in somatic hybridization experiments with potato. Allotriploid somatic hybrids between diploid tomato and monoploid potato were isolated from fusion experiments with a nitrate reductase-deficient mutant of tomato and with an albino tomato mutant. Asymmetric somatic hybrids between hygromycin resistant tomato and gamma irradiated, kanamycin resistant potato were isolated on media that contained both antibiotics. Although many hybrid calli were obtained, no viable plants could be regenerated. Tomato and potato protoplasts were also used to study the effect of gamma irradiation on karyogamy in heterokaryons, DNA fragmentation, DNA repair and DNA synthesis.