Samples of Hyperici herba were obtained by harvesting Hypericum perforatum L. in different plant development stages. The relation of flower development phases in the drug's flower fraction was examined. The HPLC method was then employed for the analysis of the content of secondary metabolites in different flower ontogenesis phases. The content of dianthrones, derivatives of quercetin and hyperforin increased from the first bud phases (0.29%, 0.80%, and 2.47%, respectively) to flowers just opened (1.04%, 4.23% and 6.60%, respectively). The content of dianthrones and quercetin glycosides then decreased (in unripe fruits 0.11% and 0.08%, respectively), whereas the amounts of hyperforin increased to 8.07% in fruits. The content of I3,II8-biapigenin increased from 0.21% in small buds to 1.04% in buds just before opening and has then decreased gradually to a value of 0.02% in fruits. Rutin was not detected in the samples.