During the years 1977-78, the distribution of Ephemeroptera of the above mentioned families of the uper flow of river Myjava was investigated with respect to their preference of bottom substrate. The extent of abundance was studied, too. From the collections of the year 1984 - made monthly from October to March and in two weeks intervals in the rest of the year - we determined the growth diagram and the developmental cycle for highly abundant species. We determined the following species: Baetis alpinus, B. fuscatus, B. gemellus, B. lutheri, B. melanonyx B. muticus, B. rhodani, B. vernus, Centroptilum luteolum, Procloeon bifidum, Caenis horaria and C. macrura. The most abundant was the species B. rhodani. Considerable differences in development were proved when compared with literary data, especially by the species B. muticus, B. rhodani and B. vernus. These may be caused by the type of the flow, as well as by the lack of vegetation and by very law level of the water in summer.
