Alkaloid content variations were studied in four Spartium junceum populations in different dynamic stages. The highest alkaloid content was found in young plants, in reproductive organs, particularly in seeds, and in the twigs with primary structure. In addition, among the four populations, the highest alkaloid values were noted in the pioneer population, the lowest in the more vigorous population. These alkaloid contents can be interpreted as a defensive strategy of the species, and more specifically, of individuals in the pioneer population, which are the most vulnerable to predators and parasites. © 1994.