Five till ten years after once intensively used grasslands are taken out of agricultural use, the hemiparasite Rhinanthus angustifolius may locally build up a population (phase I) and becomes temporarily dominant (phase II). Rhinanthus angustifolius remains dominant for some time, whereupon the population decreases to a low level (phase III). Some aspects of population behaviour are studied experimentally in the field. In early successional stages, more seedlings established themselves where the vegetation had been cut short. During late succession fewer seedlings were found among the cut vegetation. The creation of 36 cm2 gaps reduce capsule production per plant when compared with 7 cm2 gaps, during early succession. In late succession stages no difference had been found between no gaps, 7 cm2 gaps, and 36 cm2 gaps. Total capsule production is much greater in early succession than in late succession. In the three successional stages, sward density was measured 3 times during the season. The sward density is only important in the seedling stage of Rhinanthus angustifolius. Rhinanthus angustifolius establishes itself in relatively open swards in early succession, whereas in late successional stages Rhinanthus angustifolius is not dependent on sward density.