Numerous stripeless tree frogs have colonized an artificial reservoir on Tenerife. The large number of individuals becomes apparent only after nighfall when the males gather to call, and then the chorus is uncomparably loud. The procedure of calling can be seen in two males; mating-, territorial- and release-calls with their respective behaviour are demonstrated. Females which are ready to mate allow males to clasp them and begin to lay their eggs in the form of small portions several hours later: The pairs dive at the time of laying. The females assume the laying- or signal-position, let the eggs leave the cloaca and wipe them away with their hind legs; the sinking eggs stick to plants. In addition, the film shows free-swimming larvae of different ages and some of their typical behaviour patterns.