Investigations on size and density of Triturus populations were made between 1976 and 1979 at four small waters in the surroundings of Münster (West Germany). All waters contained mixed populations consisting of two or three species (Triturus vulgaris, T. alpestris, T. cristatus). Populations of individual species varied from very small numbers to nearly 890 adults. The largest mixed population had a maximum of about 1780 adults. Density was between less than 0,1 and more than 5 specimens per m2. In the largest mixed population the maximum density was about 10 specimens per m2. Water temperature has a great influence on population density. In one population the size did not vary within the study time (four years), but in all others, population fluctuations were observed. These fluctuations were small in large populations, but in small populations small as well as great fluctuations were observed.