This Diploma thesis describes the history of tea, its charakterisic, technologic processing, chemical structure and effect on human organism, as well as requirements of legislation. This is followed by characterization of microbes which contaminate teas, products of their metabolism which have negative effects on human health (especially mykotoxins) and struglge against these microbes. Experimental part is orientated on assignment of significant groups of microbes in samples of tea in draw leaves and prepered tea.