In the mountainous regions of Middle America there are several groups of hylid frogs that inhabit mountain streams. Some of these groups, such as _Plectrohyla_ and _Ptychohyla_, have been elevated to generic rank, whereas others are retained in the large and complex genus _Hyla_. In the mountains of México five species of hylids that seem to compose a phyletic unit are herein referred to as the _Hyla bistincta_ group. Since 1955 I have been accumulating specimens of, and data on, this group with the result that all specimens known to me, including the types of all named taxa, have been studied. Detailed observations have been made on the ecology and life histories of three of the species; the other two species are known to me only from preserved specimens.