The life cycles of nine species of mayflies were elaborated on basis of collected material. A winter cycle with one generation a year was found for all the investigated species of the genus Rhithrogena (R. carpatoalpina, R. puytoraci, R. gorganica, and R. wolosatkae). The remaining species analyzed had in this period summer cycles with one generation (Ephemerella ignita), winter cycles with one generation (Baetis muticus, Habroleptoides confusa) or a winter cycle with two generations a year (Baetis rhodani).