Attention of researchers and plant breeders was turned to Helianthus debilis debilis since 1985. This species seems to have taken part in allopolyploid differentiation of Helianthus genus. In order to get information on interspecific hybridization in the genus Helianthus we have studied four accessions, H. debilis debilis, H. annuus Ha 89mt. F1 hvbrid and F2 selfed line. Chromosome number analysis that revealed the occurrence of aneuploid chromosol me number was performed; in root and shoot tips. F the parents, the occurence of diptoid number is superior to thet in the hybrids. Microdensitometric analysis of nuclear DNA content of shoot and root apices showed variability in DNA values.