Hypericum perforatum L. in vitro cultures with different morphological characteristics referred to shoots, calli and cells were used as experimental models for studying of secondary metabolite productions. To determine whether production of secondary metabolites could be enhanced, in vitro cultures were exposed to exogenous application of phytohormones and chemical elicitors (jasmonic acid, salicylic acid, pectin and chitin). To assess responses to biotic elicitors, cells were treated with mycelia from three fungi Fusarium, Phoma and Botrytis. Shoot cultures exhibited a higher yield of secondary metabolites, but calli and cells showed remarkably fast and strong response to applied elicitor. Secondary metabolite production in cells can be partially changed by supplementation of these elicitors and well controlled cultures could be used as a source for rapid and increased production of hypericin and pseudohypericin. This book is intended for graduated students and researchers in Plant Cell and Tissue Culture and Plant Molecular Biology. Students and researchers who are just beginning to work in this field will also find much valuable information in this book.