Parasitic weeds supply their demand of water, carbon and nutrients from host plants, severely affecting the crop growth, biomass partitioning and causing major yield losses. The impact exerted by parasite depends on the host and parasite species/genotypes, particularities of their interaction, developmental stage, as well as environmental factors. İn the most of cases the degree of damage to the host is dependent on attack intensity. İn this regard, the effect of broomrape (Orobanche cumana Wallr.) populations on biomass production and distribution in sunflower was investigated. The experiments were performed under controlled conditions, in greenhouse, using a sunflower hybrid susceptible to broomrape (Performer) and fourteen populations of O. cumana with different level of aggressivity. The results indicate that O. cumana infestation significantly reduced the biomass accumulation in host plants (by about 20.4-57.1% lower than in uninfested control). No significant correlations were found between this parameter and the intensity of the attack, but it strongly correlated with the amount of biomass of parasitic plants per host plant (r=-0.53). The parasite strongly reduced the host aerial biomass (by 32.0-58.7% compared to the control), high negative correlations (r = -0.52) between this parameter and the intensity of the attack being observed. İnfection also suppressed the accumulation of root parasite biomass (by about 32-49.0%). İn addition, it has been established that the combined biomass of the pathosystem (total biomass of host and parasite) was significantly less than that of the uninfected plants. Thus, biomass losses can be only partially explained by parasitic sink activity and, also, may be due to the negative effects on host photosynthesis. Moreover, O. cumana changed the biomass allocation patterns. The values of the shoots: root ratio was lower compared to uninfested control, indicating on the distribution of biomass preferentially to underground part of the host plant, which is the unique point of parasite attachment, in detriment of the aerial parts. These results are in agreement with previous reports regarding other root parasites.